General info on 10-meter Data

under construction

For most areas, the most detailed USGS maps are 7.5-minute topo sheets. Each map covers an area 7.5 minutes (one-eighth degree) by 7.5 minutes. Along with other information, the maps contain contour lines of constant elevation at 40-foot intervals. In maps of low slopes, the the interval may be as low as 5 feet. A map of 40-foot contours may have supplemental contours on flat coastal areas, and it may drop contours in extremely steep areas. In a small proportion of maps, the contour intervals are metric.

All the contour lines have been scanned and vectorized (converted to polylines). Some maps are posted as DLG files, but most quads never got beyond the internal Tagged-Vector-File format. Many quads were converted 30-meter DEMs, with elevations (in integer meters) at 30-meter intervals. The "level 2" 30-meter DEMs are not bad. "Level 1" DEMs are made through other means, and are bad. You can ususally recognize them by the horizontal stripes that show up in shaded-relief or slope maps. Although level 1 30-meter quads are still posted at this site, the mosaicked 30-meter maps consist of resmpled 10-meter data where available.

10-meter DEMs are made from these same contour lines. They are generally not 3 times as good as 30-meter DEMs, but they do capture nearly all the information in the contour lines. You can use a 10-meter DEM to reconstruct 40-foot contours that closely match the original contours. The results would not be so good with another contour interval.

Getting 10-meter data

To zoom in on a part of the state map, click on the desired 1° × 2° quadrangle. You will see a map that quad, showing the component 7.5' quads. Some of the names on the map my not be consistent of the official quad names listed in the table below. (If any names in the table are wrong, let us know.) The detailed maps on not clickable at this time. The first item in the table is the DNR row/column number. The last two digits are the column, starting with 01 designating the 7.5' quad lying to the east of the 125° meridian, and counting eastward. The first zero to two digits designate the row, starting with 1 designating a quad lying below 49° and counting southward. As Washington actually extends a few hundred meters north of 49° in some places, there are quads (such as quad 16: "Point Roberts OE N") which are row zero. Note the quads with the designation OE are overedge quads, containing slivers of data which would be printed with the adjacent quad in the world of paper maps.

The second item in the table is the official quad name, usually chosen for a major city or topographic feature. In some cases (eg. "West of Pysht") the namers found no feature of note. In some cases, a 7.5' quad is designated as a quadrant of a 15' quad. This is the primary source of inconsistent names.

The third item is another geographic code. The first 5 digits designate the SE corner of a one-degree block. The following letter and number designate the row and coloumn, counting from the southeast corner.

The fourth item is the vertical units. Most quads are stored in digital decimeters. Although data is certainly not accurate to the decimeter level, the added precision let's you calculate smoother slopes. The ARC/INFO demlattice command will import these grids as floating-point meters. Some quads in southwest Washington are stored in integer feet. These are noted with an "f".

The last column is a comment extracted from file header.

The file that you download will be up to 3 megabytes, depending on the complexity of the terrain. The file name will begin with a "q" for decimeter files, or a "f" for files in vertical units of feet. These are .zip files which are combatible with pkunzip and winzip, and can also by unzipped with the public-domain unzip program now available on windows and most unix systems. In zip archive contains one file. For example q1010.zip unzips to q1010.dem. All unzipped files are more than 8 megabytes. They are in the venerable USGS ASCII DEM format, which most commercial and public domain packages can import.

This is public-domain data from the USGS. The data is in the UTM NAD27 projection, like the paper maps. Locations will differ by a couple hundred meters from NAD83 or WGS84. Data west of 120 degrees is in zone 10; eastern data is in zone 11. A quadrangle which is square in geographic (latitude-longitude) coordinates is not even a rectangle in UTM coordinates. The sides of quad lean in toward the central meridian (123° for zone 10, 117° for zone 11, and the top and bottom edges curve upward away from the central meridian.

Rob Simmonds has just pointed out to me that the 10-meter DEMs have some gaps at the boundaries of (631) Downey Mountain, (632) Dome Peak, (730) Pugh Mountain, and (731) Lime Mountain. This problem was corrected with mosaicked data.

As of December 4, 2001, all Washington quads (except for 5 over-edge slivers on the Canadian border?) are present and indexed. There may be different version of some 10-meter DEMs in existent. We may look into the version question later.

Mosaicked 30-meter data for western (zone 10) Washington as bil files. (updated with May, 1999 data)

Mosaicked 30-meter data for eastern (zone 11) Washington as bil files.

The USGS has put up all[?] their 30-meter DEMs (in SDTS format) at http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html. The rumor is that they have temporarily withdrawn their online 10-meter DEMs because of problems representing decimeter vertical units in SDTS.

MrSID images of shaded relief plus hydro for Puget Sound and eastward (Gig Harbor to Monte Cristo)