Lesson 2

Manipulating and Summarizing Attribute Data

The following information was created from external data files containing information on housing units of different categories, including the number of units damaged or destroyed, total dollars of damage, and housing density.  This information was joined to the attribute table of counties which were affected by the tornadoes. New fields were created by summing unit statistics to create more meaningful categories and dividing unit statistics from square mileage's of counties calculated using a script provided with ArcView.   Finally, the data was presented in thematic maps using color ramps to classify the data into larger categories and the tornado paths were overlaid onto the counties using a graduated scale (graduated scale shows up better on the graduated color counties) to show the F-scale of each tornado that crossed the counties.

This map shows a distribution of the number of units damaged in the affected counties.  The map was created by calculating the total number of units reported damaged and classifying into the ranges shown below:

This map shows a distribution of the number of units destroyed in the affected counties.  The map was created by calculating the total number of units reported destroyed and classifying into the ranges shown below:

This map shows a distribution of the housing density in units per square mile of the affected counties.  The map was created by calculating the total number of housing units, dividing this by the area of the counties in square miles, and classifying into the ranges shown below: