Lesson 4: Perform a Flood Analysis with Overlay

In this lesson, you overlay two layers. One layer represents the flood zone in Redding, California. The other layer represents the enterprise (business) zone in that city. You add and label road data to see which streets are affected. Then you add a layer representing local hospitals. Use a buffer to see which streets are farthest from help in the event of a flood.

Overlay creates a layer representing the area where two existing layers intersect. Use Overlay to compare two layers that overlap in space.

You can choose from various overlay types, including the following:

• Intersect shows just the areas that the two layers have in common.
• Union shows the sum perimeter of the layers.
• Clip removes areas outside the shared area.
• Erase removes the shared areas and leaves the rest.

For a complete description of the overlay types, see About Overlays.