Sierra Nevada
Basin and Range
Desert Southwest
Rocky Mountains
Great Plains
East Coast

Holoscenes - Textures of the Earth

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The Data Sources for the Maps
All of the maps were produced using U.S. Government data sets. Many of the datasets are free and available online, some of the datasets are free but must be ordered on CDROM, some of the datasets must be purchased, some of the datasets are repackaged and sold at a modest price by various resellers.

USGS Land Use and Land Cover (LULC) Data
Based on aerial photography from the 1970's and 1980's, this dataset shows urbanized areas and various vegetation covers. This dataset provides the colorful background foundation of the maps on this site. In most cases, 1:250,000 scale data was used. Portions of the coverage is available in 1:100,000 scale.
USGS digital line graph (DLG) - Hydrography
The hydrography dataset provides the locations of rivers, streams, dams, shorelines, and canals. Most of the maps on this site use the 1:2,000,000 scale data. Because the LULC coverage also shows lakes and water bodies, but at a different scale and accuracy, the shorelines often do not coincide. In the worst cases, they were edited to remove unpleasant double edges.
USGS Digital Elevation Model (DEM)
1-degree The striking shaded relief effects are derived from the DEM dataset, which contains numeric elevations on a 1-degree grid at a resolution of 3-arc seconds. In most maps several DEM coverages were necessary. All were resampled using the map's projection to compute average elevations at each pixel and then used to generate the shaded relief.

Many of the DEM datasets are derived from digitized contour lines and retain some artifacts of this process. Several of the maps on this site reveal these artifacts, which are especially noticable in regions of low slope.

USGS digital line graph (DLG) - Transportation
The roads, trails, and railroads are from the DLG Transportation layer. As with the hydrography layer, most of the maps use the 1:2,000,000 scale data. In order to make the transportation features more visible, they are excluded from the shaded relief rendering. Although the maps on this site are not intended to be road maps, it is a fact that roads are familiar landmarks to most Americans.

It is my hope that visitors will gain a better appreciation of how the landscape directed the efforts of the engineers who built our transportation systems.

US Department of Transportation, Bureau of Transportation Statistics. National Transportation Atlas Databases (NTAD) CDROM
  Although most of the datasets on this CDROM are derived from the USGS DLG datasets, they are packaged in useful themes that can be used to obtain features such as National Park and state boundaries. A few of the maps on this site contain features obtained from these datasets.
US Department of Commerce, Bureau of the Census. TIGER/Line® Files.
  Most inexpensive road map software are based on the TIGER/Line® dataset, because it provides street names and block numbers. For rapidly changing urban environments, it is often the most up-to-date US Government source. However, the spatial quality of the data is rarely very good. The maps on this site occasionally incorporate boundary features from the dataset, especially US Government reservation boundaries or political boundaries, where shown.
USGS Geographic Names Information System
  This place name dataset provides locations and names of features such as towns, landmarks, lakes, and cultural features. In addition, it locates the source and mouth of named streams, and provides elevations of selected points. Over 2,000,000 features are available. Most of the labels on the maps in this site are obtained from the GNIS dataset.
US Department of Commerce, Bureau of the Census. Land Area, Population, and Density for Places: 1990
  Because the GNIS dataset names all places in the US, there is a need to filter the information to obtain features relevant to the scale of the map. This Census Bureau dataset provides the 1990 population of places indexed by the FIPS place codes. Using this dataset in combination with position information from the BTS National Transportation Atlas and names from the FIPS 55 standard, the population centers were identified and their labels applied to the maps in this site.
Federal Information Processing Standards Publication 55-3
  The place name coding scheme detailed in this standard is used in many of the other datasets.
US Department of Commerce, National Geodetic Survey. NGS Data Sheets.
  When various sources were in conflict regarding the position or elevation of a feature, I resorted to the Geodetic Survey's catalog of control points (the "benchmarks" familiar to Boy Scouts and Power Squadrons). These are the original survey points used to provide horizontal and vertical control of places in the US.

Although most of the data sheets are nothing more than exacting spatial references, in some cases they offer intriguing glimpses of America's past. When documenting the route to and placement of markers, the surveyors often left a record of areas that are now obscured or obliterated by modern development.

All maps and content Copyright (c) 1999-2001 James R. Irwin.