Introduction to GIS

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A Brief Overview of GIS

Numerous applications of GIS can be seen in our own Town of Amherst.

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Geographic Information Systems (GIS) are a set of computer programs that can organize, display, and analyze spatially distributed data.

At its simplest, GIS is "mapping", providing a geographic arrangement of diverse information, allowing for visual comparison.

Such maps are therefore a powerful means to educate, in class and in publications.

Additional GIS tools can extract related features, provide geostatistical analysis, and generate 3D models and movies of time-dependent changes.

GIS has been applied in geology, biology, psychology, anthropology, sociology, linguistics, history, political science, economics, and many other fields.

GIS data is commonly in one of two forms:

Raster: A grid of rows and columns of colored cells.

These might represent photographic or scanned images.

Vector: A geometric shape, including points, lines, and polygons.

These might represent buildings, roads, and counties.

Either of these can have tables of data associated with them, e.g. elevation, population, financial values, etc.

These associated data can be used to color a map so that it conveys information with visual impact.

Some samples of GIS-produced maps for the town of Amherst are shown below, clear evidence of its cross-disciplinary value.

The data underlying these maps comes from many sources: the Town of Amherst, the State of Massachusetts, the U.S. Census Bureau, and the U.S. Geological Survey.

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Overview Maps
Visible Orthographic Photograph	Scanned Map	Infrared Orthographic Photograph
Amherst's true colors are revealed by this orthophoto (a photo with perspective removed). It's a mosaic of many taken by airplane. Cell Resolution = 0.152 m = 6 in.	A scanned USGS topographic map shows streets, buildings, open lands (green), and constant-elevation contours (brown lines). Cell Resolution = 2.54 m = 8.33 ft = 100 in.	A Landsat 7 satellite image shows warmer areas (purple) and cooler areas (green), with streets added for reference (black). Cell Resolution = 291 m = 955 ft.
Type: Raster/Image.	Type: Raster/Image.	Type: Raster/Image; Vector/Line.

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Scientific Maps
Terrain Elevation (Topography)	Water Resources (Hydrography)	Vegetation
This "digital elevation model" (DEM) gives each pixel a color-coded elevation (black = 90 ft., white = 1302 ft.). Cell Resolution = 30 m = 98 ft.	Lakes, reservoirs, and streams in blue, over the DEM to illustrate relationship to land forms.	Different types of vegetation, e.g. forest, grasslands, agricultural, etc.
Type: Raster/Data.	Type: Raster/Data; Vector/Line, Polygon.	Type: Vector/Polygon

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Demographic Maps
Population	Age	Income
Census 2000 population. Each dot represents 10 people (distributed randomly within census blocks, also shown).	Census 2000 average age within each census block, grouped into four categories.	Census 2000 average household income within each census block group, grouped into four categories.
Type: Vector/Polygon.	Type: Vector/Polygon.	Type: Vector/Polygon.

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Civil and Political Maps
Streets, Precincts, and Schools	Land Use	Open Lands and Trails
Streets and railroads, voting precincts (blue), and K-12 schools.	Different uses of land, e.g. commercial, residential, agricultural, institutional, etc.	Open lands (green) and trails (red), and again water(blue).
Type: Vector/Line, Polygon, Point.	Type: Vector/Polygon.	Type: Vector/Line, Polygon.

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Calculated Maps
Non-English Principal Language	School Buffer Zones	Watersheds
Census 2000 population whose principal language is not English, normalized by the total population (applied to census block groups).	Schools surrounded by 1500-ft. buffer zones.	Analysis of digital elevation model to determine regions that flow into the same stream (in random colors), with streams superimposed (light blue).
Type: Vector/Polygon.	Type: Vector/Line, Polygon, Point.	Type: Raster/Data; Vector/Line, Polygon.

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Course Overview

Because of its diverse applications and multiple data types, learning GIS can take several classes.

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First Class: Introduction and Constructing Maps

You will learn to construct maps using GIS data such as the above.

You will discover how to use GIS for exploratory analysis of geographic data.

The data has been prepared (geographically referenced) in advance so that you can focus on the general skills required to work with it.

Often geographic data is not ready-to-use, and in subsequent classes you learn how to use these different formats.

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Second Class: Sharing Maps and Mapping Place Name Data

You will also learn how to export your maps into a number of formats such as PDF or Google Earth, so that it can be shared with others who don't have this GIS software.

You will then learn to map data from tables that use names for geographic locations.

This includes census data and street address data.

In these simple tables, information about each geographic region is in a single row, viz. its name and attribute data.

This type of data can be geographically referenced by associating it with existing prepared data.

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Third Class: Mapping Coordinate Data

You will learn about geographic spatial references and how the globe is projected onto flat maps on computer screens and paper.

In the process you'll learn to map another common tabular format for geographic data that uses X-Y coordinates such as latitude and longitude.

The data collected by a Global Positioning System (GPS) receiver is in this format.

This type of data can be geographically referenced by associating it with descriptions of its spatial reference (i.e. how its coordinate system is oriented in space).

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Fourth Class: Mapping Raster Data

You will learn about the basic characteristics of rasters, which represent a regular grid of data covering the Earth’s surface. Examples include aerial or satellite photos, scanned maps, and digital elevation models.

Their regularity and coverage allow rasters to be used in calculations to determine characteristics such as watersheds — regions of land where water flows downhill and through a particular location (usually the mouth of a stream or river).

You will also learn how to georeference scanned paper maps, which still provide a lot of information about our world; when brought into a GIS they can be overlayed with other data for comparison.

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Fifth Class: Editing Map Data and Geostatistics

Scanned maps usually include features that you may want to extract, e.g. houses, roads, property boundaries, etc. With ArcGIS’s vector editing tools, such features can be traced into new sets of GIS data.

Editing tools also allow you to work with existing vector data to transform it in various ways, e.g. merging or splitting polygons, reshaping lines, etc.

Geostatistics is the application of statistics to the characterization and modeling of geographically distributed data. It is based on the observation that locations generally have similar characteristics, implying that they are not independent of each other.

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Academic Uses of GIS

There are many different ways that GIS can be used in academic pursuits.

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As seen in the previous section, there is a wide variety of data that can be used to build your own maps.

Finding this data and pulling it together in a usable format is typically the largest effort involved in GIS.

For example, data from the Third World or precise historical data can be difficult to come by.

As a result, the most effective academic uses of GIS are:

1. Faculty research and student thesis projects that are longer term and so may include the development of original data or the pursuit of uncertain data sources.
   
   (An Economics thesis project utilizing British census data is shown to the right.)
2. A "term map" where students learn to build their own maps over a semester (though it may be helpful if data is identified in advance).
   
   (A map produced in a class focused on the urban and educational history of Cambridge, Massachusetts is below left.)
3. Simple classroom activities that are prepared in advance for students, to allow them to explore an issue with geographic foundations (often these can be prepared with ArcGIS and then deployed with the free ArcReader or the more familiar Google Earth software).
4. Maps created to illustrate important ideas that are provided to students in lectures or handouts or on-line.
   
   (For example a map that illustrates the economic and political alignments in the 2006 Mexican presidential election, shown below right.)

The Reference Librarians will be of great assistance in obtaining existing data, and Academic Technology Services can assist you in all of these activities.

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The ArcGIS Software

The ArcGIS software that Amherst College provides has made "desktop GIS" a reality.

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Geographic Information Systems have been around for more than sixty years, but have become increasingly accessible as computing power has increased.

Amherst College has one of the best GIS available, the Arc products from Environmental Systems Research Institute commonly referred to as ESRI.

Their current software, ArcGIS, has made GIS significantly easier than it was even a decade ago.

There are also a large number of extensions, for example for spatial or three-dimensional analysis.

ArcGIS is available on all Windows computers in most campus computer labs, as well as on classroom projection computers.

Faculty, staff, and students can install ArcGIS on any Windows computer where they are administrators, from the Amherst Software Collection.

Contact Academic Technology Services for more information or assistance.

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Additional GIS Training and Resources

There are many other options for learning GIS and extending your knowledge.

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Amherst College's license for the ArcGIS software includes a number of online courses prepared by ESRI, accessible to anyone with an Amherst College account. Contact Academic Technology Services for more information.

The folder G:\Shared Drives\Amherst Software\Maps contains a great deal of data provided by ESRI, the town of Amherst, and the state of Massachusetts, that can be used as the foundation for your own maps.

There are a number of tutorials that can be found on the Internet, some of which are:

• ESRI's on-line documentation.
• GIS for Geoscientists: a course from Hamilton College oriented towards geoscience majors.

ESRI also provides a useful collection of tips and shortcuts for the Arc software.