GIS For Dummies®

Chapter 14

Exploring Topographical Surfaces

In This Chapter

Using topography to identify what you can and can’t see

Working with stream basins

Understanding the relationship of topography to flow

Identifying the parts of a stream

Topography deals with the configuration of the Earth’s physical surface and landforms, their characteristics and locations, and their graphic depiction on maps. Topographic surfaces can be flat and uniform, or deeply dissected by streams and their associated watersheds or drainage basins (areas that drain in the stream). Some topographic surfaces are gentle and rolling, moving fluids slowly, and others are rough and steep, causing fluids to move rapidly with great erosive force.

You can find a staggering number of forces that create diverse land surfaces, as well as different surface types. Fortunately, earth scientists have grouped, summarized, and generalized most of these forces and their resulting effects to produce some pretty substantial models that you can use. In this chapter, I show you three basic groups of models based on topographic surfaces: viewshed analysis, basin analysis, and stream morphometry (stream shape analysis).

Modeling Visibility with Viewsheds

Analyzing terrain so that you can identify places that are (and aren’t) visible from a known location on the earth is called viewshed analysis. Just like a watershed is a place where you can find the presence of water, a viewshed is a place where you can observe an object in your line ...