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.
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.
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.
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.
What are the file formats for the National Atlas map layers and data
- 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).
- 1 vector map layers are also available in ESRI file geodatabase format.
- A limited number of vector map layers may be available in Arc/Info Export format.
- Some map layers are actually images. These are distributed in GeoTIFF
- 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.
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"
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.
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.
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.
Incorporated -- Argus
-- AutoCad Map 3D
Incorporated -- MAPublisher
Incorporated -- MicroStation
Cadcorp SIS Product Suite
for the Web, Maptitude
for Great Britain
Clark Labs, Clark
University -- IDRISI
Research Institute (ESRI) -- ArcGIS Explorer,
ArcGIS Explorer Online (free downloads),
ArcGIS for Desktop
ERDAS -- ER
Analysis Support System (GRASS) (free download)
Software LLC -- Global
-- Modular GIS Environment
Manifold Net Ltd.
Map Maker Desktop
Mapping -- Map Maker
PCI Geomatics Group
Incorporated -- Freeview
(free download), Geomatica
Pitney Bowes Business Insight
Army Corps of Engineers Coastal and Hydraulics Laboratory -- Groundwater
Modeling System (GMS)
United States Geological
Survey -- dlgv32
Pro (free download)
States Naval Academy, Department of Oceanography -- MICRODEM
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
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
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
For older GeoTIFF files, here is the projection definition for the Lambert
Azimuthal Equal-Area map projection.
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.
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.
|National Atlas File Naming Convention
||Digits 1-6: File Name (alphanumeric)
Unique theme name (producer defined). This will not begin with a number
and any indication of geographic region will occupy the fifth and sixth
alphanumeric character positions.
elev48i0100a.tif (100-meter resolution elevation in the conterminous
elevaki0100a.tif (100-meter resolution elevation in Alaska)
||Digit 7: Topology/File Type (character)
l = line
p = polygon
x = point
m = mixed line, polygon, point combinations
i = raster image
t = table
||Digits 8-11: Scale or Resolution (numeric)
010 = 1:1,000,000-scale
020 = 1:2,000,000-scale
025 = 1:2,500,000-scale
075 = 1:7,500,000-scale
100 = 1:10,000,000-scale
150 = 1:15,000,000-scale
4000 = 4 km resolution
1000 = 1 km resolution
0540 = 540 meter resolution
0270 = 270 meter resolution
0200 = 200 meter resolution
0100 = 100 meter resolution
File names of vector map layers and data tables include 11 alphanumeric
characters. Raster image file names include 12.
||Digit 12: Projection (character)
a = Albers Equal-Area Conic
g = Geographic
l = Lambert Azimuthal Equal-Area
||File Name Appendage Indicating File Format (alphanumeric)
e00 = ESRI Export
gdb = ESRI geodatabase
shp = ESRI Shapefile
tif = GeoTIFF
dbf = dBase table
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
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."
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.
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.