In the tables above, o48123h1 refers to a 7.5' quad lying in the block northwest of 48°N,123°W. The quad is in row h (from the south) and column 1 (from the east). Quads beginning with k (There are only 4 in Washington.) are 15' wide. Quads beginning with c cover the 1°×2° block of 128 small quads, and quads beginning with f cover a 30" by 60" block. The data file is named o48123h1.zip, and will unzip (sometimes automatically, depending on your browser) to o48123h1.tif and o48123h1.tfw. The latter is a short ASCII file which enables some software to know where (in UTM NAD27) the image lies on the earth.

The second column refers to the number of quadrangles. As the Canadian border is actually slightly north of 49° across most of Washington, there is an over-edge quadrangle "Point Roberts OE N", covering the sliver of the US north of 49°. There is a special DEM file for this. However, there is no paper map by that name. The Point Roberts quad and the over-edge quad are on the same paper map sheet, hence in the same DRG file. There are also overedge quads that are mostly water, and a Dungeness quad that straddles two 7.5' quads. The 15'-wide "k" quads also are treated like this.

The DNR numbering scheme comprises a row number (starting with row 0 above 49°) and column number (starting with column 1 just east of 125°). Leading zeros on the row are dropped.

I hope that I have all the official names here. Where DRG comprised two 7.5' quads, either quad name will appear in the table.

Files will unzip to about 2.5 times their zipped size. The unzipped .tif file will be in a non-proprietary "compressed" form.