An Introduction to Geographic Information Systems (GIS)
What Is GIS?
GISs are computer hardware and software systems designed to input, store, analyze and present geospatial data. Geospatial data include most any kind of information which can be linked to a particular place relative to the surface of the earth. This includes much of the data traditionally represented on paper maps, as well as other information more often associated with tables of text or computer databases.
As Joseph Berry has put it, a GIS must be capable of four things:
- Creation of digital abstractions of the landscape (encoding).
- Efficiently handling these data (storage)
- Developing new insights into the relationships of spatial variables (analysis)
- Creating "human-compatible" summaries of these relationships (display)
Flatland
All major GIS systems function using two-dimensional geometry - a planometric view. Three-dimensional objects are represented as fixed points, lines, polygons or grid cells at one point in time, relative to the surface of the earth. This simplification imposes some rather significant limitations - for example in representing plants whose complex three dimensional structure is changing over time. However, other tools such as CAD and 3D modelers provide ways of performing these tasks, and the simplification greatly facilitates processing and analysis.
I like to think of GIS systems as the marriage between computer graphics packages and databases. Imagine that you wish to create a map of the US depicting the unemployment rate in 1988. In a computer graphics program, you can create a graphic object but cannot specify any non-graphical information about the object or change its visual properties based on object-specific information. For example, you could draw a map of the US coloring each state as you liked, but you could not assign state names to the objects you created except as separate text labels. Imagine that you obtained a table of unemployment rates by state from the census bureau. In a database, you could view the table and sort it by state name or rate, but you would not see any spatial patterns.
If you wanted to recolor the map to show which counties had relatively high unemployment rates, you would have to develop a legend describing the relationship between colors and numeric values, then recolor each graphical object (state) with the appropriate color or pattern. If you did this by hand, you would be exactly imitating the main display function of most GIS systems.
What Isn't GIS?
The most common misconception about GIS is that it is simply computerized cartography. It is easy to see how this misconception came into being, since paper maps are the most tangible end product of a GIS system. However, there are at least two capabilities of GIS that differ from traditional cartography - the ability to retain and store vast amounts of information about geospatial objects, and a large suite of analysis tools. It turns out that having a strongly cartographic perspective when building a GIS database tends to lead to the irretrievable loss of a great deal of information useful in later analysis. It also turns out that the process of generating good cartography from most GIS systems is rather challenging.
Strengths of GIS
- Allows us to create models of our environment and of our cumulative impacts on those environments.
- Automation allows rapid creation/updating of traditional paper maps
- Facilitates/allows map analyses otherwise too cumbersome to attempt
- Allows planning to occur at broad scales, based on site-specific criteria
- Allows analyses of potential alternative futures
Weaknesses of GIS
- Expensive to develop and to maintain (although often cheap compared to the alternatives...)
- Requires significant training and computer hardware/software.
- Handles 3D data poorly
- Handles change over time poorly - tends to focus on static views
- Multiple complex and incompatible file formats
Examples of GIS Projects
Chernobyl Project
WV Futures
Spotted Owl Habitat Modeling
The President's Forest Plan
The Course Project
Background - The Muddy Creek Project
- how it got started
- project goals
- geoscoping
- current status
- relationship between the research project, studio course and this course.
GIS based on 1930s airphoto interpretation
Layers to be created:
- vegetation
- landuse
- transportation
- Hydrography
Database creation process
- scan airphotos
- mosaic into flight lines
- mosaic into single base photo
- orthocorrect and georeference base photo
- digitize into either current classifications or aggregates thereof
using either Photoshop->PICT->macGIS or macGIS directly.
Analysis
Landscape description
- how did the landscape function in 1930?
- how does it function today?
- how has it changed over time?
Evaluation/Suitability Models
- Are current land uses appropriate?
- How could salmon (pond turtle, etc.) habitat be maintained or restored.
- What alternative land use practices are feasible for the area?
- What alternative practices/crops might be economically profitable and environmentally beneficial?