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Lakota Studies 400/600:  Special Topics:  Introduction to Geographic Information Systems and Science

Week 6 Notes:  GIS Core Analysis Functions 

Core Spatial Analytical Functions within GIS

A GIS is distinguished from other types of information systems because of its spatial analysis functions. You have already performed many of these functions this semester. The core functions that are unique to GIS can be broken down into those that work on the spatial data, those that work on the attribute data, and those that work on both the spatial and attribute data together. The list below is not meant to be an all-inclusive list of GIS functions, but only some of the major ones.

The first group of functions, those that work on the spatial data, include mosaicking--combining several adjacent data sets into one file, as well as thinning coordinates, and edgematching discrepancies along the edges of map files. Geometric transformations assign real-world coordinates to data, or to adjust one layer so it will overlay onto another layer, in a process called registration. Probably the most common spatial function is format transformation--you might have data in one format, but you need it in another. For example, if your colleagues are using GeoMedia GIS software, either you or they will probably convert the data into ArcView format (shapefiles or coverages) so that you can use it. Another example is converting raw data such as an elevation grid from a USGS Digital Elevation Model (DEM) into a grid that can be manipulated in your GIS software. Another spatial function is the creation, edit, or deleting of spatial features, or parts of features. This could include the digitizing of a new portion of a road, for example.

The second group of core functions works on the attribute data.  You have already queried the attributes of many tables of data this semester, such as earthquakes, soils, and population.  Fields and rows in tables can also be edited, added to, and deleted.

The third, and most common, group of functions works on the spatial and attribute data together. These include classifying data to create the desired map. You have already classified data according to natural breaks, quantiles, standard deviation, equal interval, equal area, and user-defined classifications.  Measurement allows the user to calculate the distance along an arc, the area of a polygon, or the distance between points or along a grid cell.  Overlay operations are another core GIS function.  You have already performed one type of overlay, an intersect, when you were choosing the study sites for needle grass, Stipa comata.  Clipping one data set based on the extent of another is another common overlay operation, and union is still another--combining polygons based on a spatial characteristic or attribute.  Neighborhood operations are core functions as well, and they include searching adjacent areas based on a criteria, and topographic functions, including the computing of three-dimensional models, slope, the direction of slope (aspect), and the creation of isolines, or lines of equal value.  Connectivity functions are other core functions, and they include proximity--such as when you created buffer zones around South Dakota rivers.  Contiguity functions are another subset of connectivity, used to measure how adjacent areas are connected.  Network functions include routing and allocation; for example, how to effectively route school buses around Todd County to pick up and drop off students.  Spread and search functions determine how difficult it is to traverse an area.  These functions have been applied for such diverse applications as a chemical spill and flood control models. Computing viewsheds is another way to determine how things are connected.  For example, if you wanted to build a cell phone tower on the Rosebud lands, where would you decide to locate it so that people relying on it will have the best reception?

We'll have the opportunity this semester to explore many of the above functions.

Back to SGU GIS Course Home

Author:  Joseph J. Kerski, Geographer, USGS, jjkerski@usgs.gov, 303-202-4315