Fundamentals of GIS
To be able to use transcad efficiently, it is necessary to understand some fundamentals of GIS. Two of the most important GIS concepts are introduced here to facilitate the understanding of the tutorial materials. More GIS concepts will be introduced throughout the quarter.
- Maps are generated from a database
Although GIS display maps, in most cases these maps are not stored in computers as image files. Maps are generated by GIS from a database with different tables. For example, each node in the map (Figure 1) is generated based on the coordinates in the Nodes table (on the upper right hand side). Each street link is generated by linking the two end nodes (see the Highways/Streets table).
- Features are organized into layers
A map can be regarded as a set of overlaying transparencies. Each transparency is drawn with one type of feature. For example, in Figure 1, the map consists of two layers: Nodes and Highways/Streets. Each layer is associated with a data table and each feature is linked to a record in the table.
transcad Tutorial
See page 15 to 23 of the transcad User's Guide
Figure 1 Map and Database
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