Introduction to Computer Mapping
Raster Data (satellite image)
Vector Data (TIGER data)
Computer mapping uses the speed and versatility of computer graphics to display spatial data. Digital map data consists of two fundamental types: vector and raster. The type of data determines how it will be stored and displayed.
The basic principles of cartography apply to computer mapping, with some modifications. Computer maps still have scale, although the computer can easily change the display scale. Even when the display scale changes, the underlying scale at which the data was collected cannot change. Because the earth has a three dimensional shape and the map (or computer screen) is a two dimensional flat surface, the cartographer must use a projection to transform three dimensions onto two. Finally, using multiple data sets requires consideration of datums, because all coordinates depend of the reference frame in which they are considered.
To help portray three dimensions on two, maps frequently use isolines, or lines of constant value of a parameter. Contour lines represent isolines of elevation as used on topographic contour maps, and the term contouring has been extended to the general process. Computer contouring uses the computer for fast, consistent contouring.
Approximate conversions, degrees to metric.
Last revision 2/15/2015