UNITED STATES DEPARTMENT OF INTERIOR
U.S. Geological Survey
Color Shaded Relief Map of the Conterminous United States
by Paul Schruben
USGS Reston, VA
Open-File Report 99-11
DRAFT
DISCLAIMER
Although program tests have been made, no guarantee (expressed or implied) is made by the authors or the U.S. Geological Survey regarding program correctness, accuracy, or proper execution on all computer systems.
Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. This report is preliminary and has not been reviewed for conformity with the U.S. Geological Survey editorial standards.
Reston, Virginia
January, 1999
Availability:
The color shaded relief maps of the conterminous U.S. are available as an Open-File Report CD-ROM and on the internet at the following site:
https://pubs.usgs.gov/openfile/of99-011/
Processing Techniques:
The color shaded relief map of the conterminous U.S. was created from 15 arc-second digital elevation model (DEM) data. The data set traces its origins back to the early 1960's when .01 inch scans of 1:250,000 USGS topographic sheets were produced by the Defense Mapping Agency and converted to 3 second data by the USGS National Cartographic Information Center. The 15 second grid cell data (Michael Webring, written communication) used in this report dates from the mid-1980's with occasional local and regional updates. The 3 second grid nodes were averaged with a 6x6 operator and decimated to 15 second grid cells which is about the resolution of the original .01 inch data set. The 3 second data is available as 950 separate 1x1 degree quadrangles from the USGS EROS Data Center web site.
The elevation data portrayed in these maps contain many artifacts due to the quality of the source data and limitations of the processing techniques. Spikes were eliminated by setting a range based on local histograms or shaded relief plots. In relatively flat areas such as California's San Joaquin Valley, the edges of DEM blocks are clearly visible. Errors in elevation of 20 meters are common and appear magnified due to the five-fold vertical exaggeration used in the hillshading described below.
The 15 arc-second DEM files were converted to Environmental Systems Research Institute (ESRI) ARC/INFO GRID format and merged into a single grid. The grid was masked to the detailed U.S. border supplied with ESRI's ArcView 3.0. It was projected to Albers conic equal-area meters using cubic convolution interpolation. The projection parameters are:
Projection ALBERS Units METERS Spheroid CLARKE1866 Parameters: 1st standard parallel 29 30 0.000 2nd standard parallel 45 30 0.000 central meridian -96 0 0.000 latitude of projection's origin 23 0 0.000 false easting (meters) 0.00000 false northing (meters) 0.00000
The image file "nearest_bilinear_cubic.bmp" shows the effects of the three types of resampling algorithms available in ARC/INFO: nearest neighbor assignment, bilinear interpolation, and cubic convolution.
The longitudinal extent of a 15 arc-second grid cell varies over the north-south extent of the conterminous U.S. from approximately 303 meters in northern Minnesota to 422 meters in Key West, Florida. The images on this disc were sampled at 468, 400, and 300 meters. The "apparent" resolution continues to improve below 300 meters, even though sampling beyond the original resolution is merely interpolation. While the effect of oversampling is visually appealing, the file size becomes very large. The image file "resolution_comparo.bmp" demonstrates the benefits of finer sampling rates. Both maps in the image are from the same 15 arc-second data and are shown at 500k scale.
The hillshading was multi-directional from azimuths 225, 270, 315, 360. The sun angle was 30 degrees. Single-direction hillshaded maps are also included on the disc. In single-directional shading, the sun direction was 315 and the sun angle was 45 degrees. The multi-directional shading shows more detail but is darker. The following RGB colors were assigned to 10 elevation classes:
meters ASL red grn blu -999 -1: 0 135 66 dark green 0 29: 0 189 98 30 74: 68 235 133 75 149: 116 255 174 150 299: 176 255 203 lt green 300 499: 255 222 154 tan 500 999: 255 197 127 beige 1000 1749: 237 167 101 light brown 1750 2499: 217 146 93 dark brown 2500 9999: 255 255 255 white
The NODATA cells were converted to white. The three RGB grids were converted to a single 24-bit-per- pixel tiff file and a tfw "world" file. All the above processing was done in ARC/INFO.
The 24-bit tiff was converted to an 8 bit tiff in Adobe Photoshop. The quality of the color rendition suffered significantly in this step. See the image file "color_comparo.bmp" . In this file, the top image is 24-bit color, the middle image is 8-bit index color with dither, and the bottom image is 8-bit index color, no dither. All the images on this disc are 8-bit, non-dithered. The Photoshop tiff's were then saved as Paintshop Pro tiff's which draw faster in ArcView.
Available projections and resolutions:
The map is available in three resolutions and in two coordinate systems. The 300 meter resolution map is size 146mb. Smaller 400 meter and 468 meter maps are also included on the disc. The map is available in Albers meters and unprojected decimal degrees.
Here is a summary of the maps on the disc:
File name size(mb) projection cell size shading scale us15a300m.tif 146 Albers meters 300m multi-dir 500k us15a300s.tif* 146 Albers meters 300m single-dir 500k us15a400s.tif 82 Albers meters 400m single-dir 600k us15a468m.tif 60 Albers meters 468m multi-dir 750k us15g280m.tif 182 decimal degrees 10" 200-280m multi-dir 500k us15g420m.tif* 80 decimal degrees 15" 300-420m multi-dir 750k * These files are zipped.
Other files on this disc:
color_comparo.bmp comparison of coloring techniques geo2alb.prj projection parameter file for US Albers meters nearest_bilinear_cubic.bmp shows effects of 3 resampling techniques resolution_comparo.bmp shows same source map at different resolutions us.rmp remap file for 10 elevation classes us.cmp rgb color map for 10 elevation classes Webring_ascii.zip DEM source data converted to GRID-compatible ASCII
The procedure for creating us15a300m.tif follows:
Unzip Webring.zip. These files have already been run through dg2asc.exe, a DOS compatible conversion utility.
arc asciigrid w076n34.asc w076n34 asciigrid W076n40.asc W076n40 asciigrid w086n24.asc w086n24 asciigrid w086n30.asc w086n30 asciigrid w086n40.asc w086n40 asciigrid w096n28.asc w096n28 asciigrid w096n30.asc w096n30 asciigrid w096n40.asc w096n40 asciigrid w106n25.asc w106n25 asciigrid w106n30.asc w106n30 asciigrid w106n40.asc w106n40 asciigrid w116n30.asc w116n30 asciigrid w116n40.asc w116n40 asciigrid w125n32.asc w125n32 asciigrid w125n40.asc w125n40 /* This step merges them into a single 75mb grid grid us15 = merge(w076n34,w076n40,w086n24,w086n30,w086n40,w096n28,w096n30, w096n40,w106n25,w106n30,w106n40,w116n30,w116n40,w125n32,w125n40) q kill w076n34 all kill W076n40 all kill w086n24 all kill w086n30 all kill w086n40 all kill w096n28 all kill w096n30 all kill w096n40 all kill w106n25 all kill w106n30 all kill w106n40 all kill w116n30 all kill w116n40 all kill w125n32 all kill w125n40 all /* Clip with dtl-st, ESRI's high resolution coastline furnished with ArcView 3.0 shapearc dtl-st st-esri clean st-esri # 1E-7 1E-7 polygrid st-esri stg Cell Size (square cell): .004166666666 /* this is 15 arc seconds grid us15m = selectmask(us15,stg) us15p = project(us15m, geo2alb.prj, cubic, 300 q /* Re-set map extent to minimum map extent of conterminous states /* Saves processing time and makes tiff file size much smaller tables sel us15p.bnd calc xmin = -2361000 calc ymin = 260000 calc xmax = 2263000 calc ymax = 3175000 q grid us15r = reclass(us15p,us.rmp) huegrd = color2hue(us15r, us.cmp) satgrd = color2sat(us15r, us.cmp) /* No shading, just colors. Skip this step if you want shading valgrd = color2val(us15r, us.cmp) /* skip if you want shading /* Single directional shading. Skip this step if you want multi-dir shading hill = hillshade(us15p, #, #, #, 5) /* skip if you want multi-dir shading valgrd = slice(hill, eqinterval, 50, 50) /* skip if you want multi-dir shading /* Multi-directional shading shade225 = hillshade(us15p, 225, 30, shade, 5) /* these grids are 100mb each shade270 = hillshade(us15p, 270, 30, shade, 5) shade315 = hillshade(us15p, 315, 30, shade, 5) shade360 = hillshade(us15p, 360, 30, shade, 5) h03 = focalmean(us15p,circle,30)/*it takes about 1 day to make this 750mb grid asp = aspect(h03) /* this makes a 750mb grid kill h03 all asp1 = con(isnull(asp), 293, asp) /* this is a 750mb grid kill asp all w225 = sqr(sin((asp1 - 225) div deg)) /* these grids are 750mb each w270 = sqr(sin((asp1 - 270) div deg)) w315 = sqr(sin((asp1 - 315) div deg)) w360 = sqr(sin(asp1 div deg)) kill asp1 all setcell minof /* the next step creates a 750mb grid temp = w225 * shade225 + w270 * shade270 + w315 * shade315 + w360 * shade360 kill shade225 all kill shade270 all kill shade315 all kill shade360 all kill w315 all kill w360 all kill w225 all kill w270 all shade4 = int(temp div 2) /* this step creates a 110mb grid kill temp all valgrd = slice(shade4, eqinterval, 50, 50) /* this is a 110mb grid kill shade4 all
Open the tiff file in Adobe Photoshop. Select Image menu, Mode, Index color. Select Adaptive, 8 bits/pixel, 256 colors, No dither. Save as tif, no compression. This converts 24-bits-per-pixel to 8 bits and cuts the file size by two thirds. Open the tiff in Paintshop Pro and save it again. ArcView will draw this 146mb image in 10 seconds.
Credits:
Thanks to the following people who helped create the map:
Michael Webring, USGS Denver
Supplied the original 15 arc-second DEM's.
Jeff Grossman, USGS Reston
Wrote the program used to convert the Webring data to a GRID-compatible ASCII file and discovered the Paintshop Pro tiff draw-speed advantage.
Robert Mark, USGS Menlo Park
Developed the multi-directional shading technique in GRID.