Detailed National Atlas Data Download Help

Nearly all of the map layers in the National Atlas are also available for download using File Transfer Protocol (ftp). There is no charge for this service. Most of the older map layers were compiled at a scale of 1:2,000,000 or a ground resolution of one kilometer. With the introduction of 1 - the National Atlas digital cartographic frameworks at 1:1,000,000-scale - in July 2012, some map layers are now available at one million-scale. Most map layers cover the full geographic extent of the United States. Generally, vector National Atlas Data files are available in Shapefile format. Some vector map layers are also offered in Arc/Info Export and ArcGIS Geodatabase formats. Please note that we no longer offer map layers in the Topological Vector Profile of the Spatial Data Transfer Standard. Image files are available in the georeferenced tagged image file format (GeoTIFF). Data tables are distributed in the DBF format.

You can use the online, interactive Map Maker to preview the map layers. Though the map layers are compressed for delivery to you, many of these data files are quite large and can take a very long time to download. We no longer offer our data on compact disc.

Frequently Answered Questions for National Atlas Data Downloads

• What is 1?
• How do I learn more about a  particular map layer or data table before downloading?
• Are the map layers compressed?
• How do I get software to  "decompress" them?
• What are the file formats for  the National Atlas map layers and data tables?
• When I decompress a Shapefile map layer, I get at least four separate files. What are these?
• What kind of software do I need  to do anything with National Atlas map layers?
• Who offers software that  supports map layers in the Shapefile format?
• Some map layers, such as  Butterfly Occurrence, are listed as "DBF" files. What are these?
• Some map layers, such as Land  Cover Diversity, are listed as "GeoTIFF" files. What are these?
• Why aren't these files automatically georeferenced when I bring them into ESRI's ArcGIS?
• Can I order the map layers on  disc or tape?
• How can I understand your file  naming convention?
• What is "metadata?"
• Why is there more than one map  layer for some themes (such as water features)?
• How can I learn more about the  National Atlas of the United States?

What is 1?
1 is the way we market our latest digital cartographic frameworks at 1:1,000,000-scale or 100-meter resolution. These fundamental map layers provide tightly integrated, authoritative map information on boundaries, surface waters, transportation, and population centers, elevation, and land cover.

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How do I learn more about a particular map layer before downloading?
You will find links to separate Web pages that describe the contents of each map layer in the first and third columns of the National Atlas Data Download Table. The first column links to a concise introduction to the map layer. The third column links to its complete National Atlas Data Documentation file, which complies with the Federal Geographic Data Committee (FGDC) Content Standard for Digital Geospatial Metadata.

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Are the map layers compressed?
Yes. The map layers were compressed using the tar and gzip utilities. We also use the tar utility to combine two or more files into a single file for download. National Atlas Data Documentation in text format is also bundled up with each data file.

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How do I get software to "decompress" them?
Search the Web for "zip utility" and select one that supports tar and gzip on your computer.

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What are the file formats for the National Atlas map layers and data tables?

1. Vector map layers are available in the Shapefile format introduced by Environmental  Systems Research Institute (ESRI). Here is a link to a technical whitepaper for the Shapefile format in Portable Document Format (PDF).
    
2. 1 vector map layers are also available in ESRI file geodatabase format.
    
3. A limited number of vector map layers may be available in Arc/Info Export format.
    
4. Some map layers are actually images. These are distributed in GeoTIFF format.
    
5. Sometimes, what appears to be a map layer is not a map layer at all. That's true of the data tables that contain information about the occurrence of moths and butterflies in the  United States. These tables are released in the dBase file format. They can be used in any  software programs (such as spreadsheets and data base managers) that can read a generic dBase file. However, if you want to map this information (using a desktop mapping program, for instance), you must use these data tables in conjunction with the One Million-Scale County Boundaries map layer since this species occurrence information is recorded by county.
    

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When I decompress a Shapefile map layer, I get at least four separate files. What are these?
At a minimum an ESRI Shapefile consists of a main file, an index file, and a dBASE table; we have added a fourth file that provides a map layer's National Atlas Data Documentation. The main file, the index file, the dBASE file, and the description file all have the same prefix ("airprtx020," for example). The suffix for the main file is ".shp". The suffix for the index file is ".shx". The suffix for the dBASE table is ".dbf". And the suffix for the metadata file which describes the data is ".met" or ".txt".

There may be other files present. These include spatial bin files, spatial bin index files, and projection files. The file name suffixes for these are ".sbn," ".sbx," and ".prj," respectively.

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What kind of software do I need to do anything with these map layers?
The map layers and images can be used in desktop mapping, computer-aided drafting and design, image processing, and in geographic information systems. These files will not work with many common types of software you may use at home or in the office (including word processors, spreadsheets, and data base managers). We have provided a basic online geographic information system (GIS) that allows you to view and query the map layers using your web browser. Follow this link to the National Atlas of the United States Map Maker.

Data tables may be loaded and analyzed using most database or spreadsheet software. However, if you wish to produce a map using data in a table, then you must use its corresponding map layer and mapping software. For example, you may download the data table on Supplemental Nutrition Assistance Recipients and then analyze them using a database management system or a spreadsheet program. Since the data in this table is arranged by counties, you must download the One Million-Scale County Boundaries map layer in order to produce the latest maps of supplemental nutrition assistance recipients.

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Who offers software that supports map layers in the Shapefile format?
The following organizations have products that allow you to open, translate, manipulate, analyze, and/or display National Atlas map layers in the Shapefile format. We list the organization name first and then the titles of any software products that are known to (at a minimum) read Shapefiles. We suspect this list is not complete and welcome any information we can use to update the list.
Argus Interware, Incorporated -- Argus ONE
Autodesk, Incorporated -- AutoCad Map 3D
Avenza Systems, Incorporated -- MAPublisher
Bentley Systems, Incorporated -- MicroStation
Cadcorp SIS Product Suite -- Cadcorp SIS
Caliper Corporation -- Maptitude, TransCAD, Maptitude for the Web, Maptitude for Great Britain
Clark Labs, Clark University -- IDRISI
Environmental Systems Research Institute (ESRI) -- ArcGIS Explorer, ArcGIS Explorer Online (free downloads), ArcGIS for Desktop
ERDAS -- ER Mapper
Geographic Resources Analysis Support System (GRASS) (free download)
Global Mapper Software LLC -- Global Mapper
Intergraph Corporation -- Modular GIS Environment
Manifold Net Ltd. -- Manifold System GIS
Map Maker Desktop Mapping -- Map Maker
MicroImages -- TNTmips, TNTedit, TNTview, TNTmips Free (free download)
PCI Geomatics Group Incorporated -- Freeview (free download), Geomatica 2013
Pitney Bowes Business Insight -- MapInfo Professional
United States Army Corps of Engineers Coastal and Hydraulics Laboratory -- Groundwater Modeling System (GMS)
United States Geological Survey -- dlgv32 Pro (free download)
United States Naval Academy, Department of Oceanography -- MICRODEM (free download)

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Some map layers, such as Butterfly Occurrence, are listed as "DBF" files. What are these?
Using the online, interactive National Atlas Map Maker, you can select and display maps of butterfly and moth occurrences by county. These maps are creating by using data tables containing information about moths and butterflies in conjunction with a map layer that shows county boundaries. These "DBF" files are data tables that contain information about all butterfly or moth species in America, by county. These tables are used in conjunction with one of the County Boundaries map layers to map the occurrence of moths and butterflies throughout the United States. In order to use these tables within a desktop mapping or geographic information system, you must also download a County Boundaries map layer and use a relational data base manager to relate or join the map layer to the appropriate table. For more detailed information about the relationship between our County Boundaries map layers and the butterfly and moth occurrence tables, please review their information files shown in the first and third columns of the National Atlas Data Download Table.

DBF tables can also be loaded and analyzed using most database and spreadsheet software.

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Some map layers, such as Land Cover Diversity, are listed as "GeoTIFF" files. What are these?
Some National Atlas maps are actually images. Image data may also be referred to as raster data. An image consists of regularly spaced squares (also known as pixels) in which a value is assigned to each square. Each of these squares represents an area on the ground. The values can represent any characteristic assigned to that square such as an index of land cover diversity, elevation, or annual precipitation.

GeoTIFF is an acronym for georeferenced tagged image file format. The Tagged Image File Format (TIFF) is a commonly used format for storing map images. GeoTIFF refers to TIFF files which have geographic information embedded within the TIFF file. This geographic information can then be used to position the image in its correct location in the world and on the screen of a geographic information display.

TIFF and GeoTIFF are supported by most image processing programs, such as Geomatica and ERDAS.

You may follow this link for technical information about the GeoTIFF file format.

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Why aren't these files automatically georeferenced when I bring them into ESRI's ArcGIS?
Newer data files are automatically georeferenced by your software, but older ones are not. The short answer to your question relates to proprietary changes ESRI made to its published specification for shapefiles and its implementation of georeferencing in image files. In the early days of the National Atlas, these provided a competitive advantage to ESRI. Now nearly all vendors of GIS and desktop mapping software support automated georeferencing using the ESRI file format extensions.

For older shapefiles, here is the projection definition that can be used with ESRI's ArcGIS.

For older GeoTIFF files, here is the projection definition for the Lambert Azimuthal Equal-Area map projection.

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Can I order the map layers on disc or tape?
No. Map layers from the National Atlas of the United States^® are no longer available on compact disc or digital versatile disc.

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How can I understand your file naming conventions?
Information in the following table explains our file naming convention. Of course you may choose to rename these datasets once you've downloaded them. The names of our vector files and data tables include 11 alphanumeric characters. The names of our raster image files include 12 alphanumeric characters.

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What is "metadata?"
Metadata is "data about data." National Atlas map layers are georeferenced. That is, the lines, points, and areas on our maps refer to some specific place on the Earth's surface. For a digital map, satellite image, or other georeferenced information to be useful it may be necessary to know its name, location, author or source, date, data format, resolution, etc. The Federal Geographic Data Committee (FGDC) is working with industry and state and local government to develop voluntary standards for metadata. The FGDC developed and published the Content Standard for Digital Geospatial Metadata. When you download and decompress a National Atlas map layer, the file with a name that ends with ".met" or ".txt" is a metadata file that conforms to this FGDC standard. You may also display a hypertext markup language (HTML) version of this file by clicking on the file name shown in the third column of the National Atlas Data Download page."

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Why is there more than one map layer for some themes (such as water features)?
On maps, some features in the real world are represented by enclosed areas, some features are represented by lines, and some are represented by points. For example, a large lake may be drawn as an enclosed area, a stream may be symbolized as a line, and a spring may be represented as a single point.  A shapefile can only contain one type of feature, points, lines, or areas.  This means that for some of the themes there are multiple map layer shapefiles bundled in the compressed file. 

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How can I learn more about the National Atlas of the United States?
Click on this link to the National Atlas of the United States home page.

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