These .zips contain the latest version of EPA's 4km, 12km, and 36km spatial 
surrogates
for the U.S. and portions of Canada and Mexico. 

The Shapefiles used to create these surrogates are available from:
ftp://ftp.epa.gov/EmisInventory/2011v6/v1platform/spatial_surrogates/shapefiles/

The 12km surrogates are being used in the 2011v6.2 emissions modeling
platform.


The following surrogates are missing from the 4km set:

- 507 (Heavy Light Construction Industrial Land), used for onroad off-network refuse trucks

- 526 (Residential Non-Institutional), used for onroad off-network motor homes

- 700 (Airport area), used for airport gasoline storage in nonpt

Surrogate 
  700 is also missing from the 36km set.



The 4km set has three additional onroad off-network surrogates - 251, 252, and 
253 - 
which are not used. These three surrogates are not in the 12km or 36km 
sets.



The 12km .zip includes a surrogate description file (SRGDESC), which can also

be used with the 4km and 36km sets, with the following exceptions:

- Missing surrogates 507, 526, 700 (see above)

- Oil and gas surrogates (681-698) have different filenames in each set