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GIS For Dummies® by Michael N. DeMers

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Chapter 7

Managing Multiple Maps

In This Chapter

Knowing the importance of managing multiple maps

Figuring out what map-handling capabilities you need

Choosing a system for your needs

If a picture is worth a thousand words, a map is worth a million. With GIS, you can work with more than one map at the same time. So, GIS gives you many millions of words at your fingertips. Every portion of the Earth, whether it’s natural or man-made, is very complex. Even if you ignore for a minute that every portion of land has depth, you can map many possible features, including houses, people, insects, plants, diseases, pollen, sidewalks, gas lines, salaries, streets, temperature, and pressure. The list is endless.

When mapped, each of these features provides a portion of the geography of a piece of land, and each set of similar features represents a separate theme. Within each theme, the explicit locations of each object, combined with the thousands of possible implicit spatial relationships, tells volumes. But, like any story, your land needs many characters — many themes. To get a complete picture, you need to have many mapped layers.

ESRI provides software, lessons, and technical support for K–12 Education around the world as a means of encouraging spatial thinking. The K–12 educators at ESRI call the map-layering process “making an Earth sandwich.” And, like an Earth sandwich, a GIS works only when it has more than one layer. The individual layers become useful only when you can extract ...

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