Geographic Information Systems

Constructing Maps

Previous: Introduction to GIS

Next: Sharing Maps

ArcGIS Pro is an easy-to-use program to display map data, symbolize it in useful ways, and output it to common, shareable file formats.

Topics

Procedures

Getting Set Up
Navigating ArcGIS Pro
Map Layer Attribute Tables
Exploring Map Features
Labeling Map Layers
Symbolizing Map Layers
Using Multiple Layers
Finding Prepared Data

Getting the Tutorial Data
Showing File Extensions
Initializing ArcGIS Pro
Saving a Project
Opening a Project
Adding Prepared Data to a Map
Viewing a Map Layer’s Attribute Table
Sorting Attribute Table Records
Locating Attribute Table Records on the Map
Selecting Features
Identifying Features
Finding Features
Labeling A Map Layer
Normalizing Data
Creating a Layer File
Symbolizing a Point Layer Using Proportional Symbols
Adding a Basemap to a Map
Finding Data on ArcGIS Online

This tutorial will guide you through constructing, coloring, and saving a simple map using ArcGIS Pro, the primary component of ArcGIS, using prepared data. In the process of doing this, you will become familiar with some of the menus and procedures you would use to create maps using your own resources.

Getting Set Up

Since this tutorial will be using specific maps and data, the next step is to make your own copy of the tutorial data.

You can use your own computer if it has ArcGIS installed, or you can use the Virtual Computing Lab (VCL), which provides a remote Windows computer with ArcGIS.

Procedure : Getting the Tutorial Data

If you are using your own Windows computer, you will need to have Google Drive for Desktop (GDD) installed, so that you can use files on Google Drive through a network-attached disk. Download it and follow the instructions here: Google Drive for Desktop.
Open Google Drive for Desktop. On most computers, GDD will appear as a link on your desktop. On your local Windows computer or a College computer, GDD will also appear in the File Explorer as the network drive G:(and that is how it will be referenced in the following instructions. In the VCL, there will also be a link to GoogleDrive in the File Explorer’s Quick Access area. The menu item Google Drive will also always be available in the menu Start.

Note: the first time you open Google Drive, in particular in the VCL, it may take some minutes for its contents to appear.
In GDD, open the folder Shared drives, then the folder Amherst Software, then the folder Maps, and finally the folder Introduction to GIS. Copy the subfolder Constructing Mapsby selecting it (clicking on it once) and typing ctrl-C (hold down the key ctrl and press C),
In the File Explorer (where the folders are), open a new window by typing ctrl-N, and navigate to a location with fast access where you can store the tutorial data:

If you are using your own own computer and have a lot of free disk space (> 1 GB), navigate to your local drive C:. Consider a folder like your Desktop rather than your Documents, as the latter is often a link to the network drive OneDriveand may require network access.
If you are using the VLC or a shared computer and are on campus, navigate to your network drive QuickAccess > GoogleDrive\My Driveor G:\My Drive.

Create a new personal folder named ArcGIS Course (for example) by right-clicking in this location and menuing New > Folder.
For better performance, right-click on your course folder and in its contextual menu select the item Offline access> Available offline, which will keep a local copy of your files in sync with the network files.
Open your course folder and paste in the folder Constructing Maps by typing ctrl-V.

The folder Constructing Maps contains the following files, amongst others:

`states.shp`	`counties.shp`	`cities.shp`	`gtopo_1km.tif`
`states.dbf`	`counties.dbf`	`cities.dbf`	`gtopo_1km.ovr`
`states.prj`	`counties.prj`	`cities.prj`	`gtopo_1km.tfw`

Note that many of these files have the same root name, e.g. states; this means that they must all stay together to work properly.

If you don’t see the period and the following text, known as a file extension, your computer is still in Windows’ default mode of hiding them. The different file types are distinguished by their icons and a description that appears if you View a folder with Details.

The first three sets of data are known as shapefiles (although only one file has the extension .shp), which is one of the basic data formats that is understood by ArcGIS. The fourth is a raster file, an image in TIFF format that actually contains elevation data.

Recommended: By default, Windows hides file extensions, but it’s better to leave them visible to more easily distinguish file types.

Procedure : Showing File Extensions

In the task bar at the bottom of the screen, click in the field Type here to search, and then start typing show file extensions.
In the search menu that appears, click on the item Show File Extensions (System Settings).
In the dialog Settings, in the section File Explorer, next to the item Change settings to show file extensions, click on the button Show settings.
In the dialog File Explorer Options, in the tab View, uncheck the box Hide extensions for known file types.
Click the button OK.

Warning: Since some — but not all — of the ArcGIS programs have trouble handling file names with spaces or special symbols, do not rename the provided folders and files unless necessary.

Navigating ArcGIS Pro

Beginning with ArcGIS Pro

Procedure : Initializing ArcGIS Pro

Click on the menu Start.
On Windows 11, you will be presented with “popular” apps, so click on the button All apps to bring up the older application menu.
Scroll down the menu and click on the item ArcGIS, and then click on the menu item ArcGIS Pro.
ArcGIS Pro will take a while to load. Eventually you will be asked to sign in:

Click on the button Your ArcGIS organization’s URL.
You should see the button Amherstcollege; if not, type it in (no space), and click the checkbox Remember this URL.
Click the button Continue.
You should now see another button Amherst College; click this button to continue.
You will be asked to sign in with the normal Amherst College login screen.

Eventually, the Home window will appear:

Note the different areas of the screen: the list of activities on the left, the New Project area on top, the Recent Projects area below with its search field and the button Open another project, and the Recent Templates area on the right with the button Start with another template.

Projects are sets of files, data displays, and settings that facilitate your use of ArcGIS Pro.

Project templates are particular standard ways to start working with your data e.g. with a frequently used set of data or display such as 3D.
You should generally start by creating a new project:

In the section New Project, click on the button Map to start with a basic 2D map and basemap.
In the dialog Create a New Project:

In the field Name, type Constructing Maps.
In the field Location, click on the button Browse and navigate to the location of the folder Constructing Maps(don’t go into it), and select this folder.
Uncheck the button Create a new folder for this project.
Click the button OK.

The project should open and display all of ArcGIS Pro’s features.

The ArcGIS window is divided into four parts:

New project with a map in the middle, a table of contents on the left, and a catalog of files on the right

The larger pane in the middle is the map display area. Here there is just one map in the tab named Map, but this pane can have multiple maps, and can sometimes be split in two to present related data such as the feature attribute table.
The pane on the left is the table of Contents, which lists each map and within that map the different layers of geographic data added to it.

Here you can see the default set, the World Topographic Map, which is partially transparent, and the World Hillshade below it, which means that in the map display it appears behind the topographic map. The combination provides a pleasing representation of the terrain.
These two form what is known as a basemap, which provides a collection of standard information on top of which you can add your own data.
The pane on the right side is the Catalog, which lists the various sources of data to which you might have access, along with other project files such as maps and toolboxes.

Many of the actions you might take to work with your maps, such as symbolizing data, will display their own panes here, identified by tabs along the bottom.
The ribbon at the top provides many tools, some of which are linked to panels in the right-hand pane.

You can display other sources of “prepared” geographic data by adding them to the map.

Procedure : Adding Prepared Data to a Map

Prepared data is ready to use with ArcGIS Pro, without the need to first establish its geographic basis. The simplest way to add data is from the Catalog.

In ArcGIS Pro, in the pane Catalog, double-click on the item Folders to reveal the various folders that are directly accessible to project.

This includes, in particular, the project’s home folder , e.g. Constructing Maps, which is a good place to store data particular to the project.
Double-click on the project home folder and continue to navigate to the location of the data you want to add.
Drag the desired data file, e.g. states.shp, onto the map or to the pane Contents.

Note that only one file with this root name appears, hiding the other pieces, a simplification feature of the Catalog.

A map of the United States including Alaska and Hawaii should now appear in the map display pane:

screenshot of states

Layers

Data such as states.shp that are displayable geographically are referenced by superstructures called layers, which are listed in the pane on the left, which is called the table of Contents.

Layers are so-called because they overlay each other like transparencies when you add them to the map. In this case, the layer states is listed above the layer World Topographic Map, which means it is displayed in front of it in the map display area.

Notice what happens when you uncheck (and recheck) the box next to its name!

Maps can display several different kinds of layers: points, polylines, polygons, images, and others.

The layer states consists of polygons defining the boundaries of the fifty states and the District of Columbia. Each of these polygons is called a feature of the layer.

In addition to the location of the data, layers also store information about how to symbolize them (e.g. green filled polygons here) and how to label them.

The layer’s name, by default, is the data file’s root name, but it can be easily changed.

Experiment: Change the name of the layer states by clicking on it, pausing, and then typing something else, e.g. United States.

The view of the layers in a project map by the source of their data. The pane Contents provides multiple views of your layers, but the two most important are:

List by Drawing Order, which shows just the simple names of data layers, corresponding to what is visible (or potentially visible) in the map pane.
List by Data Source, which lists the full path names of the data files referenced by the layers.

Note that in the latter view, the two default layers, World Topographic Map and World Hillshade, are being pulled into the map from the Web.

Note: Data is not embedded in a project document, but only linked to these sources and imported into the map on the fly. That’s why it’s a good practice to keep your data together in the project, unless the data is in a standard, shared location such as an archive.

Usually you’ll want to stay in the Drawing Order view, but the Data Source view can be helpful when a data link is broken.

Project Documents

Before we proceed any further, it’s a really good idea to save your project.

ArcGIS Pro project documents store your current arrangement for use at a later time, and are especially useful after the occasional ArcGIS Pro crash — ArcGIS Pro continously stores a backup copy that can be used to update the project when you restart the program.

You’ll therefore want to continue to save them on a regular basis, for example every time you’re satisfied with the current view.

Procedure : Saving a Project

There are two ways to save a project:

In ArcGIS Pro, select the menu Project, click on the menu item Save Project, and click the button Save.
In ArcGIS Pro, at the top of a project window, click on the button Save Project.

Project documents are saved in the project’s home folder with the file extension .aprx.

You’ll also want to return to your projects later.

Procedure : Opening a Project

There are three ways to open a project:

In the Windows File Explorer, navigate to the project home folder, locate the file with extension .aprx, and double-click on it.
Open ArcGIS Pro, and in its opening screen it will list recent projects; click on the one you want, but if it’s not there, click on the button Open another projectto open a file dialog and navigate to the project home folder. This possibility will also appear if you select the menu Project and click on the menu item Open.
In ArcGIS Pro, at the top of a project window, click on the button Open Project to open a file dialog and navigate to the project home folder.

Navigating a Map

The primary tools that you will use navigate the map are located in the ribbon Map, in the section Navigate. They provide quick ways to zoom in and out, pan across the map, restore a map to its full extent, and return to previous views of the map:

Tool	Action	Control
Any	Zoom in	Point at the new location and slide two fingers towards you (trackpad) or rotate scroll wheel towards you (mouse).
Any	Zoom out	Slide two fingers away from you (trackpad) or rotate scroll wheel away from you (mouse).
Explore (or hold down `C` key)	Pan (move the map)	Click-and-drag the map to center on a new location.
Explore and hold down `shift` key	Zoom in by 50%	When the cursor changes to click on the new location.
Explore and hold down `shift` key	Zoom to a rectangular region	When the cursor changes to click-and-drag a rectangular region.
	Zoom in to current center by 20%.	Click
	Zoom out from current center by 20%.	Click
	Full extent: zoom out to the full view of all of the data.	Click
	Go back to previous map view — if you appear to lose your map, this will bring it back.	Click
	Go forward to next map view.	Click

Experiment: Try zooming in and out of the map, panning, and using the full extent button to return to the original map view. Also try using the back and forward buttons to move along the sequence of views you’ve created.

We’ll talk about some of the other tools on this ribbon later.

Map Scales

The degree to which one has zoomed in to or zoomed out from the map is commonly expressed by comparing a distance on the map to the same distance in the real world. So, for example, the distance from New York to Los Angeles is about 6 centimeters in the computer view above, but roughly 4,000 kilometers in real life. Since 6 cm = 0.00006 Km, we can calculate a ratio of these two numbers that doesn’t depend on units, 0.00006 Km : 4,000 Km = 1 : 70,000,000. This ratio describes what one map unit corresponds to in the real world, and is called the map scale.

ArcGIS Pro displays the current map scale in a text field / menu at the top of the screen just to the right of the button Add Data:

Map Scale text field / menu

Intially the scale for your map will be around 1 : 100,000,000, depending on the size of the map display pane. As you use the zoom buttons in the Tools toolbar, the scale adjusts automatically. It’s also possible to change the map scale by clicking and typing directly in the text field, or by clicking on the adjacent pop-up menu button and choosing from a list of common values.

Experiment: Observe how the map scale changes as you zoom in and out of the map. Try changing the scale by typing a number in its text box, and by choosing a value from the menu.

Note that as you decrease the second number in the map scale ratio, the scale increases. Cartographers therefore use the following terms to describe scales:

At a small scale:

the ratio is small;
the second number is large;
the map is zoomed out;
you can see a large area;
you see less detail.

At a large scale:

the ratio is large;
the second number is small;
the map is zoomed in;
you can see a small area;
you see greater detail.

Map Layer Attribute Tables

Tables, Records, and Fields

When you add a map layer, you will also bring along an attribute table describing the individual features of the map. For example, every state in the map has a name, and we may want to label them, so we need to know how those names are associated with the polygons.

Procedure : Viewing a Map Layer’s Attribute Table

In ArcGIS Pro, in the Table of Contents, right-click on the name of the layer, e.g. states.
The layer’s contextual menu will now appear; it provides many actions that apply just to this layer. Select the menu item Open Attribute Table.

Shortcut: you can also open a layer’s attribute table by holding down the Ctrl key and double-clicking on the layer’s name in the Table of Contents.
An attribute table appears in its own window floating above the map, and it looks something like the following:

screenshot of states attributes

In this table, every feature of the layer is listed in its own row or record. Each column or field represents a different attribute of these features. So, in this case, we see each state name on a different row, along with its population in 2000 and 2005, its federal information-processing code, etc.

Every attribute table will begin with the two structural fields FID and Shape. The first is a Feature Identifier that will always be a unique number to distinguish one feature from another. The second is a summary description of the geography of this feature; hidden behind the text “Polygon” there’s a lot of information about how to draw the lines that comprise it.

All other fields are optional, but their presence is important to enable the true power of GIS. These fields are usually one of two types:

Text, such as STATE_NAME; these field values are left-justified.
Numeric, such as POP2000: these field values are right-justified.

Note that sometimes fields appear to be numeric but in fact are text, e.g. STATE_FIPS, because they are stored as a sequence of individual digits.

Locating Attribute Table Records

The features in a table are often in a random order. However, you can compare them more easily with each other by sorting them by any one of the attributes in the table.

Procedure : Sorting Attribute Table Records

In ArcGIS Pro, in a layer’s Attribute table, pick a field, e.g. STATE_NAME, and double-click on its header, the name of the field at the top of its column.

Note that the column will sort itself in ascending order, from A to Z.

Double-click on the header a second time; the column will now sort itself in descending order, from Z to A.
Locate a field whose values are common to multiple records, e.g. SUB_REGION, and right-click on its header to bring up its contextual menu; you’ll see the same two options listed, Sort Ascending and Sort Descending, but instead select the third one, Advanced Sorting….
The dialog Advanced Table Sorting will now appear; it lets you choose multiple columns on which to sort in sequence:

Advanced Table Sorting Dialog

In the menu Sort by, select a field whose values are common to multiple records, e.g. SUB_REGION.
In the menu Then sort by, select a more specific field, e.g. STATE_NAME.
Click on the button OK.

Note that now all of the records are sorted according to the first field, and within each group the records are sorted by the second field.

Note that all of the data in a row stays together, even though you’ve sorted on a single column (something that doesn’t automatically happen in a program like Excel); this is a common feature of a database.

Experiment: Sort the data by different fields in the table.

Locating Map Features

Once you have found a feature in a table, you can locate it on the map in a few ways.

The most common is to select it, but you can also flash it and zoom to it.

Procedure : Locating Attribute Table Records on the Map

In ArcGIS Pro, in a layer’s Attribute table, scroll to a feature you are interested in, and click on the button Select Record at the far left end of the record.

The feature is now selected , and its record will be highlighted in an aqua color.

In addition, the feature will be highlighted in the same color on the map itself; you may have to scroll, zoom, and/or move the attribute table around to see it.

To deselect the record you can either:

Right-click on the button Select Record and then click on the menu item Select/Unselect;
In the toolbar Tools, click on the button Clear Selected Features.

In an intricate map it can sometimes be hard to pick out a selected feature, so sometimes a better way to locate it is to flash it, by right-clicking on the button Select Record and then click on the menu item Flash.
Often the best way to locate an item is to zoom directly to it, by right-clicking on the button Select Record and then clicking on the menu item Zoom To.

Exploring Map Features

The information in the attribute table can be used in a more focused way to explore map features.

Selecting Map Features

When you don’t have the attribute table open, and you recognize features on the map, you can also select them using the tool Select Features.

Procedure : Selecting Features

In ArcGIS Pro, in the toolbar Tools, click on the button Clear Selected Features; this will remove any highlighting remaining from the previous procedures.
Again in the toolbar Tools, click on the tool Select Features.
In the map pane, click on any feature you recognize, e.g. Massachusetts. The feature will be highlighted with the same aqua color seen in the attribute table.
If it’s not already, open the attribute table .
In the attribute table, click on the button Show: Selected. Now only the selected feature will appear, so you don’t have to scroll through the records to find it.

Identifying Map Features

When you don’t have the attribute table open, a quick way to get information about a particular map feature is to use the tool Identify.

Procedure : Identifying Features

In ArcGIS Pro, in the toolbar Tools, click on the tool Identify.
The dialog Identify will open; move it to a convenient location that doesn’t obscure the map.
In the menu Identify from:, choose which layers you want to select from:

<Top-most layer>;
<Visible layers>;
<All layers>;
A particular layer.

With a single layer on the map, these options all have the same effect; there will be more about multiple layers later.

Click on a feature in the map, and the data fields in its row in the attribute table will be displayed.

Finding Map Features

More often than not you won’t recognize a feature on the map, but you can find it without going into the attribute table using the tool Find.

Procedure : Finding Features

In ArcGIS Pro, in the toolbar Edit, click on the tool Find.
The dialog Find will open; move it to a convenient location that doesn’t obscure the map.
Click on the tab Features if it’s not already selected.
In the field Find:, type in some piece of information you know about the feature such as its name.
In the menu In:, choose which layers you want to select from:

<Top-most layer>;
<Visible layers>;
<All layers>;
A particular layer.

With a single layer on the map, these options all have the same effect; there will be more about multiple layers later.

In the button group Search:, choose which attribute field you want to search for this information:

All fields;
In field:, and then choose one of the available fields from the menu;

Click the button Find, and a list of matching features will be displayed at the bottom of the dialog.
Click on the feature of interest and the map will flash its location.
If you right-click on the feature of interest, a contextual menu will appear, and you can choose some other options, such as Zoom To.

Labeling Map Layers

There is, of course, a more general way to identify features on a map, and that is by labeling them on the map itself.

Every map you’ve ever seen probably includes labels that give names to the features on the map.

ArcGIS can label a layer with any of the data in its attribute table, and it will intelligently position them to avoid overlap with other layers’ labels.

The general properties of a layer, such as labeling and the data source, are controlled through the dialog Layer Properties, which you will see a lot of from this point onward.

Procedure : Labeling a Map Layer

In ArcGIS Pro, in the Table of Contents, right-click on the name of the layer, e.g. states.
The layer’s contextual menu will now appear; it provides many actions that apply just to this layer. Select the menu item Properties....

Shortcut: you can also open a Layer Properties dialog by double-clicking on the layer’s name in the Table of Contents.

In the dialog Layer Properties, click on the tab Labels, which looks like the following:

screenshot of label tab

For labels to appear on your map, you must click on the checkbox Label features in this layer.
In the section Text String, in the menu Label Field, choose which attribute you want to use for the labels.

For example, select STATE_ABBR to use state abbreviations, which are smaller than the state name and will fit the map more easily.
In the section Text Symbol, choose a font, font style, font color, and font size.

Labels appear at the chosen size relative to the computer screen and independent of the map scale, so you will probably need to adjust them when you are nearing completion of the map and know how much room you have for them.
By default labels will not overlap and will disappear when necessary. Also by default every part of a feature will be labeled (e.g. all of the Hawaiian islands). These options and more can be changed by clicking on the button Placement Properties… and making appropriate adjustments.
Click the button OK (or Apply if you want to see the effect without closing the dialog).
Once you have chosen the attribute that you want to use to label the layer, you can quickly turn the labels off and on in the Table of Contents, by right-clicking on the name of the layer, e.g. states, and then, in the layer’s contextual menu, selecting the menu item Label Features.

Zoom into the map to verify that the labels you’ve added appear at an appropriate scale.

Symbolizing Map Layers

Symbolizing Polygons Using Categories

Right-click on the map layer again and select Properties to bring up the Layer Properties screen. Now select the Symbology tab.

screenshot of symbology tab

At present, the map is colored using a single color (symbol) for every feature (state polygon). If we simply wanted to change this color, we could click on the colored rectangle and select a different color. However, what we want to do is color the states different colors. To color the states different random colors, select Categories (which will bring up a new screen), set the Value Field to STATE_NAME--because we want to give different colors to states with different names. Then choose a Color Scheme on the right that consists of patches of distinct colors.

screenshot of unique values options

Click the Add All Values button and OK. Each state will now be colored by one of the colors from the scheme you chose. You can go back to the original single color for all states through the Symbology tab by selecting Features then Single Symbol then OK.

Checklist for Coloring states random colors

Right-click the states layer and select Properties
Click the Symbology tab
Select Categories
Select STATE_NAME as the Value Field
Select a Color Scheme with patches of colors
Click Add All Values

Symbolizing Polygons Using Quantitative Fields

Right-click the states layer, select Properties and then the Symbology tab. Select Quantities on the left.

screenshot of quantitative options

Begin by selecting the quantitative variable for coloring the map as the Value in the Fields section.

Coloring a map using a quantitative variable is more complicated than coloring it using random different colors. There are three basic choices to make:

You need to select a color scheme from the ones provided. Generally you will select a color ramp whose values vary in a continuous way to indicate change in the quantitative variable.
You need to decide how many value classes you want to use. This will group the values into a discrete set of ranges.
Finally, you need to decide what method you will use to classify the values (choose the value ranges). ArcGIS Pro provides several ways to do this automatically, as well as the option of letting you set the break points between categories manually.

Classification Methods

ArcGIS Pro will by default use five categories and the natural breaks method for dividing the values into five categories. The natural breaks method tries to draw the lines between categories of values where they naturally break. If you want more categories, you can easily change the number. Usually between five and eight categories works reasonably well. If you use too many categories, the color values may be difficult to distinguish.

To use a different method of classifying values, click the Classify button over on the right side of the screen.

screenshot of classifcation screen

The quantile method creates categories with near-equal numbers of features in each. If we use it to create five categories of states and there are 51 states (50 states and the District of Columbia), we will get categories that each contain ten or eleven states. The equal-interval method divides the values into categories whose value ranges are the same. Choose one of these methods and click OK on this screen and then on the Layer Properties screen. The map will be colored--or symbolized according to the choices you made.

Checklist for coloring a map using a quantitative field

Right-click the states layer and select Properties, then the Symbology tab
Click Quantities
Select the field you want to use in Field Value
Select the number of Classes
Choose a Color Ramp
Click Classify to change the classification scheme

Eliminating the Size Dependence of Data Display

When looking at a map like the previous one, which displays population as a color spread out over the entire state, our brains automatically integrate the area, emphasizing larger states over smaller states, even if they have the same population. Compare, for example North Dakota and Alaska — which one looks like it has the larger population? They actually have the same population, with only a 2% difference.

So, instead of coloring a map with a simple numeric attribute such as “total population ” — an extensive quantity — it’s usually better to divide it by the state’s area to map population density — an intensive quantity. It’s also reasonable to map the ratio of any two extensive attributes where that makes sense, e.g. “people over 80” divided by “total population”, to find the relative fraction of an attribute, which is also an intensive quantity.

In either case, this is easily accomplished in ArcGIS by specifying the field in the denominator as a normalization field.

Procedure : Normalizing Data

In ArcGIS Pro, in the Table of Contents, double-click on the name of the layer, e.g. states, to open its dialog Properties.
Click on the tab Symbology.
The dialog Save Layer will appear. It’s advisable that you navigate to the same folder containing the shape file with which you’ve you’ve been working.
Your layer document will have a file extension of .lyr . Choose a root name describing the data and symbology in this file, e.g. states-pop2000, and click the button Save.

Such a representation of data is known as a choropleth map, from the Greek for khōra (region) + plēthos (multitude).

Exercise: Normalizing Data

Using data for the female population of each state, normalize it by the male population, and map with an appropriate symbolization.

Both the classification and normalization of your data can make major changes in the way your map looks and in the way it’s interpreted by someone who neglects to read the legend. It’s important to make these choices based on an understanding of the data, with an eye on establishing visual contrast between different data groups.

Creating Layer Files

Once you have colored a layer in a particular way, it’s sometimes useful to save that configuration for future use, such as in another map. A layer document stores a reference to a data set and how it’s currently symbolized. It can be added to a map just like the plain data set.

Procedure : Creating a Layer File

In ArcGIS Pro, in the Table of Contents, right-click on the name of the layer, e.g. states.
The layer’s contextual menu will now appear; select the menu item Save as Layer File....
The dialog Save Layer will appear. It’s advisable that you navigate to the same folder containing the shape file with which you’ve you’ve been working.
Your layer document will have a file extension of .lyr . Choose a root name describing the data and symbology in this file, e.g. states-pop2000, and click the button Save.

Using Multiple Layers

One of the most powerful features of ArcGIS is its ability to display multiple map layers at once, much like a set of transparencies allows different views to be displayed together in many combinations. To see how this works, we’ll add more and different types of data to your map, beginning with the plain states file you loaded earlier.

Procedure : Connecting to Additional Data Folders

Prepared data is ready to use with ArcGIS Pro, without the need to first establish its geographic basis. There are two ways to add such data to your map:

Adding Data From the Catalog

In ArcGIS Pro, in the pane Catalog, double-click on the link Folders to reveal the various folders that are directly accessible to project.
This includes, in particular, the project folder itself, which is a good place to store data particular to the project. Double-click on this folder and continue to navigate to the location of the data you want to add.
Drag the desired data file, e.g. states.shp, onto the map or the pane Contents.

Adding Data From the Ribbon:

In ArcGIS Pro, in the ribbon Map, look for the section Layer and the yellow-and-black button Add Data.
The special file dialog Add Data will now appear. It looks like an ordinary file dialog, but like the catalog it only displays the various folders that are directly accessible to project. In the section Project, you will see
lets you see some of your folders, viz. those to which you have explicitly connected. Once you set up these connections, the folders will appear in all subsequent dialogs, and you will thereafter have quick access to them. When you need to set up a connection:

Click on the button Connect to Folder.
In the new dialog Connect to Folder, navigate to the folder where your data is stored; in this case, it would be the folder Constructing Maps that you previously copied to your G: or C: drive.
Click once on the folder’s name.
Click on the button OK.

If necessary, navigate into the folder Constructing Maps.
Select the file states.shp; note that only one file with this root name appears, another feature of this special dialog.
Click on the button Add.

Exercise: Comparing Different Symbolizations of the Same Data File

Change the symbology of the layer states to be Features using a Single Symbol with no fill color and a thick, bright red outline .
Add in the layer file that you created in the previous procedure, states-pop2000.lyr (see the procedure Adding Prepared Data to a Map for details on adding data). It will be placed above the previous layer in the Table of Contents, which means it will appear in front of it in the map itself. It references the same data set, but includes the symbology you created previously.
In the Table of Contents, you may have noticed the checkboxes to the left of the layers’ names; they are used to turn their display on and off . Click off the upper layer’s checkbox to reveal the lower layer in the map, then click it back on again.
You can also rearrange the layers by clicking on one layer’s name in the Table of Contents and dragging it above or below another layer; this places it in front of or behind the other layer in the map.
Finally, remove the more symbolized layer to return to the original single-symbol layer:

In ArcGIS Pro, in the Table of Contents, right-click on the more symbolized layer states-pop2000.
In the layer’s contextual menu, click on the menu item Remove.

Next we’ll add a different type of data, a set of points:

Exercise: Adding and Symbolizing a Point Layer

In ArcGIS Pro, in the toolbar Standard, click on the button Add Data.
In the dialog Add Data, navigate into the folder Constructing Maps.
Note how the file icon for cities.shp shows points, indicating the type of data to be displayed. Click on cities.shp, and click the button Add.

Now many points appear on the map, indicating the different cities in the layer. By default, a point layer will automatically be placed in front of all polygon layers on the map, to avoid being covered over.
Use the tool Identify to learn more about specific cities. You may need to zoom in to spatially distinguish some cities.
In the Table of Contents, just below the layer cities, you’ll see the same symbol being used to represent the layer on the map. Click on the symbol to open the dialog Symbol Selector, and try out the available options.

Exercise: Displaying a Data Subset

Can you make just the capital cities visible on the map above? (Hint: right-clicking on pretty much anything in ArcGIS will bring up a contextual menu of available options for using it.)

Save your result as a layer file so you can easily reference it later.

The previous step only allows you to select a uniform symbology for the points in a point layer. Like polygons, it’s also possible to vary the symbol based on values in the layer’s attribute table, but in several unique ways such as changing the symbol size.

Procedure : Symbolizing a Point Layer Using Proportional Symbols

In ArcGIS Pro, in the Table of Contents, double-click on the layer’s name, e.g. cities.
In the dialog Layer Properties, click the tab Symbology.
On the left side, in the list Show:, click on the list item Quantities.
Click on the sub-list item Proportional Symbols.
In the section Fields, in the menu Value:, select an attribute to use, e.g. POP2000.
In the section Symbol, click on the button Min Value,
In the dialog Symbol Selector, choose a symbol type, a color, and a minimum size, e.g. 1.
Click the button OK.
Back in the dialog Layer Properties, click the button OK. The size of the cities’ symbols are now based on their populations.
In this symbolization the smaller symbols are placed on top of the larger ones so they are more visible, however they may still be so thick in some areas that you cannot distinguish the state boundaries behind them. One way to compensate for this is to change their transparency:

Double-click on the layer you want to change, e.g. cities.
In the dialog Layer Properties, click the tab Display.
In the field Transparent: %, type a percentage value, e.g. 50.
Click the button OK.

Procedure: Adding and Symbolizing an Image Layer

We’ll add one type of raster image, representing elevation. It will come from a local repository of map data that we maintain here at Amherst College.

In ArcGIS Pro, turn off the layer cities so that only the layer states is visible.
In the toolbar Standard, click on the button Add Data.
In the dialog Add Data, navigate into the folder Constructing Maps, and add the file gtopo_1km by clicking once on its icon and then clicking the button OK. (If you click twice on an image, it may “open” like a folder and provide its three color bands separately, depending on the type of image.) Note how its icon shows a grid of pixels, indicating the type of data (image).
In the dialog Geographic Coordinate Sytems Warning, ignore the information provided and click the button Close. We will consider the implications of this dialog later when we discuss coordinate systems.

A grayscale representation of elevation will now appear. Note that, by default, an image layer will be placed behind a polygon layer to avoid obscuring it, so initially you may not be able to see some of this layer because it is covered up by the states layer.

Raster layers have one value for each pixel, in this case representing elevation, and as with vector layers that information can also be displayed:

In the toolbar Tools, click on the tool Identify.
To avoid displaying only information about other layers (such as states), in the dialog Identify, change the menu Identify from: from the default menu item, <Top-most layer>, to another such as <Visible layers> or specifically gtopo-1km.
Click on different locations to determine their elevation.

Raster layers are displayed by assigning each pixel a color based on its value. This can be, for example, the red, green, and blue values of a photograph, each in the range 0 - 255. In the case of a single-valued quantity such as elevation, a grayscale ramp is used by default, where the elevation range shown above in meters, –407 to 8752, is mapped to the black-gray-white values 0 - 255 (the latter shows up as the stretched value in the dialog Identify). A number of other color ramps are available, e.g. , which runs from bluish green at the lowest elevations to red and then white at the highest elevations (suggesting “snow-capped mountains”).

Double-click on the layer gtopo_1km to bring up the dialog Layer Properties, click on the tab Symbology, and try out a number of different color ramps.

Question: Which two places on the surface of the Earth are pinpointed by the maximum and minimum elevations, 8752 and –407? What is the linear unit here?

The colors in the color ramp are associatd with stretch

Exercise: Setting Elevation Limits

Zoom in on New England. We know it’s mountainous here, but you won’t see much contrast because the color ramp is set to the work with all of the mountains in the world. Set a more reasonable range of elevations by finding an appropriate type of stretch for the color ramp.

Finding Prepared Data

A lot of geographic data is available from government, commercial, and other sources, often in a ready-to-use format.

Basemaps

Often you’ll want to provide background for your data, such as streets or terrain, and not have to worry about constructing it yourself.

The standard basemap we’ve already seen is provided by ESRI, the makers of ArcGIS, through Internet servers.

But there are many more options you can easily use instead.

Procedure : Adding a Basemap to a Map

Basemaps are relatively easy to add ArcGIS Pro, though it’s best to first add your own data to establish its view and ensure a good choice of background. Then:

In ArcGIS Pro, in the toolbar Standard, click on the menu arrow Add Datanext to (or menu File > Add Data), and then Add Basemap….

The following dialog will appear:
Double-click on one of these, e.g. Oceans (which will work well with a user-provided land-based elevation layer).

The basemap should be added to your map, behind most other layers.

Basemap Behind User-Provided Data

There may be multiple pieces added to the map, e.g. a Reference layer that provides labels; if these are in the way, you can turn them off.

The drawback to using an Internet server for these maps is that they can sometimes be unavailable or slow to load; you may wish to turn them off until you are ready to publish your map.

ArcGIS Online

ArcGiS Online (www.arcgis.com) is a source of geographic data in formats that are ready-to-use with ArcGIS “Desktop”.

It has datasets provided by ESRI (in particular the same basemaps as above, and others that sometimes duplicate what’s in G:\Maps), as well as many that are contributed by others.

Procedure : Finding Data on ArcGIS Online

ArcGIS Online (www.arcgis.com) can be accessed both from within ArcGIS Desktop and, more conveniently, from any web browser.

If necessary, start up a web browser:

Click on the menu Start.
Point at the menu item All Programs.
Locate your preferred web browser, Chrome or Firefox or Internet Explorer (perhaps in the folder Networking and Communications), and click on it.

In your web browser, visit the web address www.arcgis.com.
At the top of the page, click on the link Gallery.

On the page Gallery you can browse for different types of data amongst the “featured content”, but it’s generally better to search for keywords. In the upper-right corner of the page, click in the text field Search for, type one or more keywords, e.g. usa major rivers, and in the menu that pops up, click on the menu item Search All Content.
On the left side of the window, check on the box Show ArcGIS Desktop Content; otherwise everything displayed will only work within ArcGIS.com.
Scroll down to review the found items; you’ll see a number of data types:

ArcGIS Desktop 10-usable, which may be downloadable or referencible internet services:

Shapefiles and CSV tables;
Layer Packages;
Features, Tiles, WMS, KML, and Map Images, which are internet data services;
Map Documents, which are .mxd files.

These documents seem to generally include references to data inaccessible to anyone outside of the author (or a small circle), so unless you can locate all of the data within ArcGIS.com, they probably won’t be useful to you.

Web browser-viewable Web Maps. These can be fun to study and play around with, but aren’t usable with ArcGIS Desktop 10.

You can click on the titles of these data sets to get more information about them, e.g. their size, author, and any restrictions on their use.

Choose a data set from one of the first two data types, e.g. the layer package USA Major Rivers, click on menu More options and select the menu item Open in ArcGIS for Desktop.
In the subsequent file download dialog, you can open the file directly (but it will be saved in a temporary location), or you can save it first in a convenient location (e.g. the folder Constructing Maps), and then add it to your map.

The downloaded file will have the name item.pkinfo, which is a reference to the layer on arcgis.com.

As with basemaps, the drawback to using an Internet server as a data source is that they can sometimes be unavailable or slow to load; you may wish to turn them off until you are ready to publish your map.
You can create a free account with ArcGIS Online and create your own publically accessible web maps by uploading materials you create with ArcGIS (beyond the scope of this course). If you are a student, faculty, or staff member of Amherst College or one of the Five Colleges, you can Sign in with your enterprise login.

Finding Data on the Internet

It’s always worth searching the Internet for geographic data.

Much of this data must be converted into a format that ArcGIS can properly display, and working with such data will be the topic of the next few sections.

However, many sets of data are “prepared” data, i.e. they are ready to be loaded into ArcGIS and immediately displayed.

Commonly such data would be labeled as shapefiles, though they are likely to be packaged as a .zip archive that Windows will automatically open.

Another relatively new format is the geoTIFF, a standard TIFF image that’s been enhanced with geographic information.

Exercise: Mapping Interesting Data

Look around on ArcGIS Online, or on the Internet using a keyword such as shapefile or geoTIFF, to find another dataset related to your interests and map it. Would it be relevant to add other related datasets? If so, see if you can find and add them to your map. Symbolize them so that they’ll stand out relative to the other datasets on your map.