Then usable tread depth is compared to remaining tread depth in order to calculate tread wear percentages. For example, a tire that started with 10/32 of original tread depth and has worn off 4/32 (down to 6/32 of remaining tread depth) is 50% worn.
1 If you know the census tract number: Use the IRS list of 2014 Qualified Census Tracts by county. 2  If you have a street address: Visit HUD's interactive QCT Map and enter the property address to view what Census Tract the property is located.
Land_area and water_area are available for census tracts, at least when you query census.gov. Can I suggest, though, that what you really want to do is a dot density map by census tracts. Not only is this much more understandable than a quantile choropleth map, but you don't need to have the land area for tracts.