arc gis期末复习考点第十二章(3)

The global version calculates one statistic for an entire distribution, whereas the local version calculates one statistic for each feature (point or polygon).

15. The local G-statistic can be used as a tool for hot spot analysis. Why?

A cluster of high positive Z scores computed from local G-statistics suggests the presence of a cluster of high values, which is called a hot spot.

16. What does a Dissolve operation accomplish?

Dissolve aggregates features that have the same attribute value or values by removing the internal boundaries between them.

17. Suppose you have downloaded a vegetation map from the Internet. But the map is much larger than your study area. Describe the steps you will follow to get the vegetation map for your study area.

Step 1: Download or make a polygon layer of the study area.

Step 2: Perform a clip operation by using the vegetation map as the input layer and the study area map as the clip layer.

18. Suppose you need a map showing toxic waste sites in your county. You have downloaded a shapefile from the Environmental Protection Agency (EPA) website that shows toxic waste sites in every county of your state. What kind of operation will you use on the EPA map so that you can get only the county you need?

Solution 1: If the shapefile includes a field of county names, then one can run a select operation to select the county of interest.

Solution 2: Download or make a polygon layer of the county, and then perform a clip operation by using the vegetation map as the input layer and the study area map as the clip layer.