Finding Features in Vector Systems
In This Chapter
Looking at vector GIS structure
Searching with two basic strategies
Summing up what you find
Making sense of the data retrieved
The most graphically accurate method of representing maps in a GIS is the vector system (which I describe in Chapter 4). Vector systems represent geographic space by using a series of points, lines, and polygons. This method differs from raster GIS, in which geographic space is stored as a collection of squares called grid cells. Because data storage differs between raster and vector systems, the way you search for those data also differs.
Not to worry. In some ways, how you find geographic objects in a vector GIS is more like how you find them on paper maps. Vector GIS allows you to work with geographic features in a more realistic way than you can in raster systems because the points, lines, and polygons are more realistically located and correctly sized. For example
Point objects: Such as wells and houses display like they don’t take up huge chunks of space (or an entire grid cell).
Lines: Have the appropriate lengths but aren’t so thick that they’re unrealistic.
Polygons: Represent the boundaries of areas much more exactly than grid cells and don’t have that blocky, checkerboard appearance.
Some books include lists of advantages and disadvantages of vector over raster GIS, but I prefer to think of these items simply as differences. Vector GIS is different in the ways it stores data (see ...