The digital orthoimage maps available on this external hard drive were produced through
the National Geospatial Program of the U.S. Geological Survey as provisional products of
The National Map .  They are released only for use by emergency response agencies and 
field personnel, and are not approved for distribution to the general public.    

Presently, national coverage of these maps is limited almost exclusively to the Gulf and 
East Coasts approximately two counties inland from the shoreline (approximately 50 miles 
inland).  As additional maps are produced over the U.S. and its territories, they will be
made available on a FTP site.  These maps are considered provisional (i.e., non-standard 
USGS products) because product specifications have evolved throughout their production.   

Several variations of the orthoimage map were created with different image sources, 
resolution, content, cartographic characteristics, and product format.  The most significant
variations among the maps relate to the orthoimage (natural color, color infra-red, tone 
balanced, non-tone balanced), projection (equirectangular or UTM), product format (PDF, 
single- or multi-layered GeoPDF, file size (averaging 12-20 Mb with extremes from 1.3 to 63
Mb), and the number of layers shown).  There are also many content differences in the maps 
including variations in text font, size, color, and use of halos; how roads and grids are 
symbolized, disclaimer and accuracy notes, and surround elements within the map margin.  

States where a large number of maps have been produced will have more than one directory, 
for example, three directories hold the maps initially available in Texas.

Each state directory holds both a text file listing of files in that directory and an 
index map ( directory_name .pdf) displaying the quadrangles within that directory.  

Files are named using the following convention:   STATE_cellname_date_OM_ geo.pdf  
For example: FL_Tampa_2004_OM_geo.pdf
Where:
STATE  is the 2-letter abbreviation of the primary State
cellname  is the Geographic Cell Names Database name for this standard cell
date   is either the year the map was generated or date of photography 
OM    indicates the map type ( O rthoimage M ap)
geo  indicates the map is georeferenced and contains multiple layers*.   

* Note: Many quadrangles were generated before the USGS had full capability to export a 
georeferenced multiple layered GeoPDF.   In these instances the file format is PDF and 
“ geo ” is not part of the file name.  About GeoPDF - Upon opening a GeoPDF users will 
be asked about downloading a free toolbar from TerrraGo Technologies. While not necessary
for opening the file, the toolbar provides greater functionality for layered GeoPDFs.  
Useful information about GeoPDF can be found at http://en.wikipedia.org/wiki/GeoPDF . 

Technical contacts:                                  Program Contact:
Jerry Wagner           Charles Matthys                Michael Cooley
USGS, Rolla MO          USGS, Denver CO               USGS, Reston VA
jwagner@usgs.gov        cpmatthys@usgs.gov            mcooley@usgs.gov  
Phone: 573-308-3764     Phone: 303-202-4447           Phone: 703-648-5528
Fax: 573-308-3652       Fax: 303-202-4020             Fax: 703-648-4722