Spatial Thinking in Planning Practice: An Introduction to GIS

51 is formed that indicates how much resistance the phenomenon encounters as it spreads in all directions (Figure 9.6). Add a destination layer, and you can determine the “least cost” path between the origin and the destina- tion. “Least cost” can be a monetary cost, but it can also represent the time it takes to go from one point to another, the environmental cost of using a route, or even the amount of e#ort (calories) that is spent. Figure 9.6. Spread Functions. "is example shows that the shortest distance is not always the least cost distance. Source: GIS Commons. http://giscommons.org/analysis/ VIEWSHED MODELING )INTERVISIBILITY ANALYSIS* Viewshed modeling uses elevation layers to indicate areas on the map that can and cannot be viewed from a speci!c vantage point. "e non-obscured area is the viewshed. Viewsheds are developed from DEMs in ras- ter-based systems and from TINs in vector systems. "e ability to determine viewshed (and how they can be altered) is particularly useful to national and state park planners and landscape architects (Figure 9.7). Chapter 9: Raster Data Models