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GIS For Dummies® by Michael N. DeMers

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Chapter 9

Finding Information in Raster Systems

In This Chapter

Creating a map search plan

Performing a search with your GIS

Making sense of your search results

Grid-based maps indicate where geographic features are located on a geographic grid, how much space they occupy, and their locations relative to other features on the map. So, grid-based maps give you an extremely easy to understand way of storing spatial information.

With paper maps, you get the information you need by reading and interpreting the printed map. Paper maps are limited because you can layer only so many geographic features onto one map before that map becomes unreadable. For example, even though each kind of feature relates to transportation information, you can’t effectively show highways, waterways, railways, and ATC flight patterns all on one paper map. That would be one confusing map! You’d probably divide this kind of information onto separate maps. To work with more than one or two types of information, you need to gather information from separate maps — and who wants to go through that effort?

In GIS, you can comfortably map many types of information to a geographic grid because all the information can be coded into a computer and selectively retrieved for whatever subset of data you want. You use computer search and retrieval techniques to get just the information you need. The GIS may contain geographic information about all crops grown in the United States. You can retrieve just the geographic ...

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