Procedure: The attribute table of a shapefile showing counties in Oklahoma(counties.shp) was joined to a table ( countydamage.dbf) using FIPS code as the shared attribute.  Records for seventeen counties with tornado data were then selected, and converted to a new shapefile, (tornadocounties.shp).  This shapefile's attribute table was joined in turn to an additional table (countystatistics.dbf ) so that additional data could be derived.  The Calculate Geometry analyst was used to determine each county's area in square miles.

New fields were then added to this attribute table, to derive additional statistical information.  Data on apartments, previously separated by building size, was consolidated into a single field, as was data for housing size (combining single-family homes, mobile homes, and apartments).   Additional data generated was used to create the thematic maps that follow, as explained below.