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How a GIS Works - Conbining Data - Part 4

One of the greatest advantages of using GIS is its capacity to combine data from many resources—layer many themes. The image of Center County below is a combination of all three vector types layered together. Below this image is a breakdown of how separate themes and layers work.

 

Theme 1: Points

Each point represents a surface water supply location.

Any guess at how many surface water supply points there are in Pennsylvania?




Theme 2: Lines

Each line represents a Pennsylvania river.

How many miles of river do you think Pennsylvania has?






Theme 3: Polygons

Each green area within the black borders is a separate polygon, representing one Pennsylvania county.

Do you know how many counties Pennsylvania has?


Theme 4 is an example of what makes GIS such a powerful tool;
Theme 4 shows all three of the previous themes combined as a single layer.

Next is a demonstration of how to ask your layers and themes questions - this is called Querying - the most important of feature of GIS, and the reason people refer to GIS as smart maps.

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Part 5
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