Retrieving and Unpacking SDTS
Data
Tutorial and Users Manual
June 23, 1998
Neither the U.S. Government nor any agency
thereof nor any of their employees make any warranty, expressed or implied, or
assume
any legal responsibility for the accuracy,
completeness, or usefulness of any information, apparatus, product, or process
disclosed herein
or represent that its use would not infringe
privately owned rights. Reference to any specific commercial product, process,
or service by
trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its endorsement,
recommendation, or
favoring by the U.S. Government or any
agency thereof.
1. Introduction. . . . . . . . . . . .
. . . . . . . . . . .1
2. Overview of DLG/SDTS and DEM/SDTS
Data. . . . . . . . . .2
2.1 SDTS Overview. . . . . . . . . . . . . . . . . . .2
2.2 Mass Conversion of USGS Data to SDTS . . . . . . .2
2.3 Sales and Distribution Policies. . . . . . . . . .3
2.4 SDTS data organization . . . . . . . . . . . . . .3
2.4.1 DLG/SDTS Data . . . . . . . . . . . . . . .3
2.4.2 DEM/SDTS Data . . . . . . . . . . . . . . .4
3.
Summary of Data Retrieval Procedures . . . . . . . . . .4
3.1 DLG/SDTS Data . . . . . .
. . . . . . . . . . . . .4
3.2 DEM/SDTS Data . . . . . . . . . . . . . . . . . . .5
4.
Detailed Instructions for Retrieving SDTS Data . . . . .5
4.1 Create Local Directory . . . . . . . . . . . . . .6
4.2 Find and Retrieve Data . . . . . . . . . . . . . .6
4.2.1 Find and
Retrieve DLG/SDTS Data . . . . . .6
4.2.1.1
DLG/SDTS Transportation Overlay: A Special Case7
4.2.1.2 Retrieve the DLG/SDTS
Master Data Dictionary7
4.2.2 Find and
Retrieve DEM/SDTS Data. . . . . . .8
4.3 Unzip and Untar. . . . . . . . . . . . . . . . . .8
4.3.1 WinZip. . . . . . . . . . . . . . . . . . .9
4.3.2 Other tar and zip utilities . . . . . . . 10
4.3.2.1
DOS tar and zip utilities . . . . . 10
4.3.2.2
UNIX tar and zip utilities. . . . . 10
4.3.2.3
NT tar and zip utilities. . . . . . 10
5.
Problems Downloading Data. . . . . . . . . . . . . . . 10
5.1 FTP . . . . . . . . . . .
. . . . . . . . . . . . 10
6.
Conclusions and Points of Contact. . . . . . . . . . . 11
1. Introduction
Two digital cartographic products of the
U.S. Geological Survey (USGS) are vector (DLG) and
terrain elevation (DEM) data in the Spatial
Data Transfer Standard (SDTS) format.
The USGS
distributes these data sets over the
Internet as a means of promoting the standard.
The SDTS
is a relatively new format that has been
mandated for federal use. Numerous software packages
from vendors such as ESRI, Integraph and
ERDAS are able to accept data in this format.
This document is a detailed explanation of
procedures for downloading and unpacking USGS
SDTS data. DLG data sets were created by
reformatting digital line graph optional (DLG-O) data
as SDTS.
DEM data sets were created by reformatting existing data sets to the
SDTS format.
These conversions include adding metadata to
each transfer, but do not necessarily include any
update or other content changes to the
spatial data.
This document can be used as a companion to:
- dlgv32 -- Windows 95 Display Software for
DLG, DEM, and DRG Data (users manual,
version
3.5), or
- dem3d -- Windows 95 Display Software
for DEM Data (users manual, version
2.0b)
The procedures described here may also be
beneficial to users of other software.
See
http://mcmcweb.er.usgs.gov/viewers for
additional information about dlgv32 or dem3d.
2. Overview of DLG/SDTS and DEM/SDTS Data
2.1
SDTS Overview
The SDTS was designed by a group of people
representing government agencies, universities,
and private companies that all saw a
requirement for a robust way of transferring earth-
referenced spatial data between dissimilar
computer systems with the potential for no
information loss. After 12 years of discussion, development, review, and testing,
the resulting
SDTS was approved as Federal Information
Processing Standard (FIPS) 173, and now also as
FGDC-STD 002. Compliance with SDTS, also
known as FIPS 173, is now mandatory for all
federal agencies. SDTS is a transfer standard that embraces the idea of
self-contained
transfers; spatial data, attributes,
georeferencing, a data quality report, a data dictionary, and
other supporting metadata are all included
in the transfer.
The SDTS is a standard. Standards are documents that specify rules;
they are neither software
nor databases.
The SDTS is a standard for data transfer, as
opposed to a standard for data processing.
SDTS
does not replace existing Geographic
Information System (GIS) processing formats.
The SDTS is designed specifically for
spatial data. Other standards exist for
other kinds of data
(digital images, documents, electronic
signals, etc.).
The National Mapping Division of the USGS is
the maintenance agency for the standard.
Please visit the SDTS web site at
http://mcmcweb.er.usgs.gov/sdts for more information .
A single-document overview of SDTS is
available at:
ftp://sdts.er.usgs.gov/pub/sdts/articles/ascii/overview.doc or,
ftp://sdts.er.usgs.gov/pub/sdts/articles/ps/overview.ps
2.2
Mass Conversion of USGS Data to SDTS
In 1995 the USGS began converting digital
cartographic data holdings to SDTS. 1:24,000-scale
(or 7.5 minute) DEM data were converted in
early 1998. Conversion of other DEM
scales have
not yet been completed.
The 1:2,000,000-scale DLG data were revised
in 1995 and are now available in SDTS. This
includes coverage of the conterminous United
States for the following categories of data:
hydrography, transportation, boundaries
(county names are included with the transfer), United
States Public Lands Survey System, and
manmade features.
All 1:100,000-scale DLG files have been
converted to SDTS format. This includes national
coverage of the hydrography and
transportation overlays, with partial coverage of other layers.
All 1:24,000-scale DLG files have been
converted to SDTS format. Coverage
varies between
overlays at this scale, but no overlay has
complete coverage.
"All files" means all files for
which DLG data have been produced.
Coverage of 1:24,000 and
1:100,000- scale DLG data is not complete.
2.3
Sales and Distribution Policies
Most USGS data are neither online nor
free. SDTS data are a significant
exception to this
policy.
Other exceptions include 1:100,000-scale DLG-O and 1:250,000-scale
native format
DEM data.
Production, pricing, and distribution policies for native DLG-O
and native DEM data have not
changed due to the availability of SDTS
data. Data in native format are still
available from the
same sources at the same prices. Because of data conversion problems, there
are a small
number of data sets that are available in native format but not
available in SDTS. All DEM data
now offered in SDTS format are still
available in native format
2.4
SDTS data organization
2.4.1
DLG/SDTS Data
DLG-O data are derived from standard USGS
topographic quadrangles. The packaging
of DLG-
O data reflects this: each physical file
covers the geographic area of some part of a standard
quadrangle, and contains a feature set that
approximates the ink colors of a standard published
map.
Similarly, DLG/SDTS data are derived
directly from DLG-O data, and reflect the DLG-O data
packaging.
Each SDTS transfer has the same geographic coverage and same spatial
data
content as the DLG-O it was derived
from. This packaging is not dictated by
the SDTS; the
standard would allow (for example) all road
and hydrography data for a county to be contained
in one transfer, but reorganizing the data
this way would have required a large and costly
production operation, instead of a
relatively simple data reformat.
A side effect is that the DLG/SDTS data
appear more fragmented and complex than necessary.
This is not a characteristic of the SDTS,
but of policy decisions made when the USGS mass
converted DLG-O data to SDTS format.
2.4.2
DEM/SDTS Data
DEM data are derived from standard USGS
topographic quadrangles. The packaging
of DEM
data reflects this: each physical file
covers the geographic area of some part of a standard
quadrangle,
Similarly, DEM/SDTS data are derived
directly from DEM data, and reflect the DEM data
packaging.
Each SDTS Data transfer has the same geographic coverage and same
spatial
content as the original source DEM.
3.
Summary of Data Retrieval Procedures
DLG/SDTS and DEM/SDTS data are held on an
ftp site.
The base address for DLG/SDTS data is
ftp://edcftp.cr.usgs.gov/pub/data/DLG
The base address for DEM/SDTS data is
ftp://edcftp.cr.usgs.gov/pub/data/DEM
3.1 DLG/SDTS Data
There are three sub-directories in the DLG
FTP site; one for each of the three data scales.
These three scales are:
100K holds 1:100,000-scale data. The
directory contains an SDTS master data dictionary for
this scale, a readme file, and 26
subdirectories, one for each letter of the alphabet. Each of
these subdirectories holds the
1:100,000-scale quadrangles whose names start with that letter.
2M holds 1:2,000,000-scale data. The directory contains an SDTS master data
dictionary for
this scale, a readme file, and 50
subdirectories, one for each state.
LARGE_SCALE holds 1:24,000-scale data. The
directory contains an SDTS master data
dictionary for this scale, a readme file,
and 26 subdirectories, one for each letter of the alphabet.
Each of these subdirectories holds the
1:24,000-scale quadrangles whose names start with that
letter.
Each data sub-directory in turn has several
more levels of directories that reflect DLG
overlays,
data
versions, and physical packaging.
The USGS GeoData web page, at
http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
provides a user interface to the ftp
site. The web page provides several
different "views" of the
data, including lists by state, by name, and
searching by graphic index. All of
these views
eventually lead to the lowest level of the
ftp directory structure.
The Global Land Information System (GLIS),
at http://edcwww.cr.usgs.gov/webglis
provides
another way to reach these data. GLIS provides relatively powerful data
search tools.
An SDTS transfer is composed of multiple
files. DLG/SDTS transfers have been
combined into
one physical file with the tar utility, and
then compressed using gzip. See section
4.3 for details.
3.2 DEM/SDTS Data
There are four sub-directories in the DEM
FTP site. At this time, only 7.5-minute DEMs are in the
SDTS format.
15min contains no data at this time. It will hold data based on 2 by 3-arc-second
spacing.
Coverage of one DEM corresponds to a
1:63,360-scale quadrangle, used primarily for Alaska.
250 holds data based on 3 by 3-arc-second
spacing. This directory is populated
with data in
native DEM format. It contains a readme file, and 26 subdirectories, one for each
letter of the
alphabet.
Each of these subdirectories holds the 1:250,000-scale quadrangles whose
names
start with that letter.
30min contains no data at this time. It will hold 1:100,000-scale data, also
known as 2-arc-
second.
7.5 minute has the same coverage as the
standard USGS 7.5-minute cell. In some
cases, this
is not an exact match of the corresponding
topographic map. DEMs never contain
overedge
data for slivers of land just beyond the
cell boundary. This directory is
populated with data in
SDTS format. It contains a readme file and 26 subdirectories, one for each
letter of the
alphabet.
Each of these subdirectories holds the 1:24,000 or 1:25,000-scale
quadrangles
whose names start with that letter.
The USGS GeoData web page, at
http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
provides a user interface to the ftp
site. This web page provides several
different "views" of the
data, including lists by state, by name, and
searching by graphic index.
The Global Land Information System (GLIS),
located at
http://edcwww.cr.usgs.gov/webglis
provides another way to reach these
data. GLIS provides relatively powerful
data search tools.
All of these views eventually lead to the
lowest level of the ftp directory structure.
An SDTS transfer is composed of multiple
files. DEM/SDTS transfers have been
combined into
one physical file with the tar utility, and
then compressed using gzip. See section
4.3 for details.
Each DEM transfer contains a data
dictionary; there is no separate master data dictionary to be
downloaded.
4.
Detailed Instructions for Retrieving SDTS Data
This section contains step-by-step
instructions for retrieving, unpacking, and organizing
DLG/SDTS and DEM/SDTS data. The Conifer, CO 1:24,000-scale quadrangle is
used as an
example of DLG data. The Big Bull Mountain, CO 7.5-minute
quadrangle is used as an example
of DEM data.
Procedures for the other scales are similar,
but vary slightly because of different product
characteristics.
These examples show how to find data using
"FTP via graphics" capabilities on the GeoData
web page.
Users who know what they are looking for and know how to use ftp client
software
may wish to skip these procedures and go
directly to the ftp site described in section 3. Reading
section 4.3 is strongly recommended before
doing this.
4.1
Create Local Directory
Create directories (or folders) on your
local computer to hold downloaded files.
For the
purposes of these examples, we will assume
you are using a computer with the Windows 95
operating system installed. If you plan to use multiple quadrangles, it
is important to organize
the data in a file structure that will help
you keep track of all data. Create an additional
subdirectory for each quadrangle.
An SDTS transfer typically contains many
files. Keeping transfers separate by putting
each
quadrangle in its own directory is necessary
because of the way files within a DLG/SDTS or
DEM/SDTS transfer are named. Storing multiple quadrangles in one
directory may result in file
collisions, where one file may overwrite
another with the same naming convention.
For the DLG/SDTS example, create a directory
named c:\data\sdts\conifer.
For the DEM/SDTS example, create a directory
named c:\data\sdts\big_bull
4.2
Find and Retrieve Data
4.2.1 Find and Retrieve DLG/SDTS Data
A Master Data Dictionary (MDD) must be
downloaded for each scale of DLG data (100K, 2M,
and Large Scale) data you intend to
use. Detailed instructions are included
in section 4.2.1.2,
below.
To download a specific data set,
follow these procedures:
1.
Go to the USGS GeoData page at
http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
2.
Scroll down the page to Large Scale Digital Line Graphs (DLG) - SDTS
format only.
3.
Since the name of the quadrangle is known, the data could be found by
selecting either FTP
via Alphabetical List or FTP via State. However, it is
common to not know exact
quadrangle names:
Select FTP via Graphics.
4.
Select Conterminous 48 states.
5. A
simple map of the U.S. appears. Click
on the state of Colorado.
6. A
map of Colorado appears, with 1-degree lines of latitude and longitude. Click near the
center of the 1-degree cell immediately west of Denver and immediately south of
Boulder.
The next display will show approximately 30 7.5-minute
quadrangles, centered on where
you clicked your mouse.
7.
Click on the 7.5-minute cell labeled Conifer, CO.
8. A
"list" of one quadrangle appears.
(Other paths to this page may produce lists of more
quadrangles.) Select the link to Conifer,
CO.
A list of nine directories will then
appear. Each directory corresponds to
one DLG overlay.
Conifer is used in this example because all
nine overlays are available. This is
unusual for
1:24,000-scale data; most quadrangles have
fewer than nine overlays finished.
9.
Select the second overlay (in this example), hydrography.
10.
Select version_1, the most recent version.
The file D3910530_hy0s.1.sdts.tar.gz
contains the SDTS transfer for the hydrography layer of
the Conifer, CO quadrangle. For an explanation of the file naming
convention, see
http://edcftp.cr.usgs.gov/pub/data/DLG/LARGE_SCALE/00README
11.
Select the file D3910530_hy0s.1.sdts.tar.gz for downloading
12. Save it to the c:\data\sdts\conifer
folder. The file can be renamed (for example,
conifer.tar.gz). Retaining the .tar.gz extensions is strongly recommended. Some browsers will
attempt to rename this file for you. In some cases, this renaming causes problems
for
decompression software. One common case is a rename from *.tar.gz to
*_tar.gz, which
confuses the WinZip decompression program.
Repeat steps 9 through 12 for all overlays
of interest.
4.2.1.1 DLG/SDTS Transportation Overlay: A
Special Case
While you're at the FTP site getting data
for the conifer, CO quadrangle, pull up the
transportation subdirectory, and click on
version_1.
You will see that it contains three DLG/SDTS
transfers: roads (the rd0s file), railroads (the rr0s)
file),
and miscellaneous transportation (for airports, pipelines, etc)(the mt0s
file). All DLG-O
1:24,000-scale sales units are packaged this
way, and that packaging was retained in the SDTS
version of the data: three separate SDTS
transportation transfers were created for each
quadrangle.
The data for these transfers must be kept in separate directories. Untaring two or
more transportation transfers for the same
quad in the same directory will cause file collisions
and loss of data.
If you intend to use more than one of these
three transportation layers, create subdirectories for
each of them. For example, c:\data\sdts\conifer\railroad. This step need not be done before
downloading the data, but must be done
before unzipping and untaring the data (section 4.3).
In 1:100,000 and 1:2,000,000 DLG data, the
three transportation overlays are combined into one
file, and therefore comprise only one SDTS
transfer. Creation of additional
transportation
subdirectories is not necessary for these
scales.
4.2.1.2
Retrieve the DLG/SDTS Master Data Dictionary
Each SDTS transfer is required to have a
data dictionary, specific to that particular transfer's
scale.
Because the DLG/SDTS data were created by reformatting DLG-O data, the
same data
dictionary can be used for all data sets of
the same scale. Rather than include
this dictionary
with each transfer, one data dictionary is
stored for all transfers at the top of the ftp directory
tree.
To retrieve the MDD:
1.
Go to http://edcftp.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
2. Scroll down the page to Large Scale
Digital Line Graphs (DLG) - SDTS format only.
3.
Click on single tar file.
4.
Save it to the c:\data\sdts\conifer folder
This file must be unzipped and untared like
other SDTS data. Placement of the data dictionary
files may be software dependent. If using dlgv32, the files may be placed in
any directory on
your hard drive, including the directory
that holds the other SDTS data files. If using ESRI
Arc/Info, place the data dictionary files in
the masterdd directory as specified by ESRI
documentation.
4.2.2 Find and Retrieve DEM/SDTS Data
1.
Go to the USGS GeoData page at
http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
2.
Scroll down the page to 7.5-Minute Digital Elevation Model (DEM) - SDTS
format only.
3.
Since the name of the quadrangle is known, the data we're looking for
could be found by
selecting either FTP via Alphabetical List
or FTP via State. Since it's common to not know exact
quadrangle names, make the selection FTP via
Graphics.
4. A
simple map of the U.S. appears. Click
on the state of Colorado.
5. A
map of Colorado appears, with 1-degree lines of latitude and longitude. Click on the bullet
right next to Colorado Springs. The next display will show approximately 30
7.5-minute
quadrangles, centered on this mouse click.
6.
Click on the 7.5-minute cell labeled Big Bull Mountain, CO.
7. A
"list" of one quadrangle appears.
(Other paths to this page may produce lists of more
quadrangles.) Select the link to Big Bull
Mountain, CO.
The file 30.1.1.934296.tar.gz contains the
SDTS transfer for Big Bull Mountain, CO.
For an
explanation of the file naming convention,
see
http://edcftp.cr.usgs.gov/pub/data/DEM/7.5min/00README
8.
Select the file 30.1.1.934296.tar.gz for downloading.
9.
Save it to the c:\data\sdts\big_bull folder. The file can be renamed
(for example,
bigbull.tar.gz). Retaining the .tar.gz extensions is strongly recommended. Some browsers will
attempt to rename this file for you. In some cases, this renaming causes problems
for
decompression software. One common case is a rename from *.tar.gz to
*_tar.gz, which
confuses the WinZip decompression program.
4.3
Unzip and Untar
The DLG/SDTS and DEM/SDTS data were designed
in 1994, before the release of Windows 95
and before most PCs were powerful enough to
use GIS data. The data were designed
for the
scientific computers of the time, which were
mostly UNIX workstations. The files in
each SDTS
transfer were combined into one file with
the UNIX tar utility, and this combined file was then
compressed using the gnu-zip (gzip)
utility. This technique for combining
and compressing files
is common on the UNIX operating system.
Tar
and gzip are not as common in the PC world, but a variety of freeware,
shareware, and
commercial implementations of these
utilities exist for all PC operating systems.
4.3.1
WinZip
One of the most common PC compression
programs is the shareware program WinZip
( http://www.winzip.com). WinZip will unzip and untar DLG/SDTSand
DEM/SDTS files if
proper procedures are followed. These instructions are for WinZip 6.3 for
Windows 95, using
the WinZip Classic interface (as opposed to the
Wizard; this is a user-selectable option in
WinZip).
Ensure that the file has a name of the form
*.tar.gz NOT *_tar.gz
1.
Start WinZip
2.
From the toolbar, select Options
3.
Select configuration.
4.
There is a checkbox labeled "TAR file smart CR/LF
translation". Ensure that this box
is not
checked.
5.
Select OK to exit configuration.
6.
Select Open from the tool bar. A
popup window appears.
7.
In the "Types of files" subwindow, select All Archives.
8.
Navigate to the local directory you created earlier
(c:\data\sdts\conifer for DLG/SDTS data or
c:\data\sdts\big_bull for DEM/SDTS data)
. A list of the files downloaded from
the USGS
GeoData site should be visible. Select one of these files and click Open.
9. A
window appears with the message "Archive contains one file .decompress it
to a
temporary folder and open it?" Select Yes.
10.
A list of .ddf files will appear.
These are the files contained in the SDTS transfer. To select
all files in the transfer, click on the
first file, then shift-click on the last file.
11.
Select Extract from the tool bar.
12.
A popup window labeled "Extract" appears. Enter, or navigate to, the path and
directory that
you want to place the data into. The extracted files are stored in the same
directory as the
compressed files, so enter (or navigate to)
the local directory you created earlier
(c:\data\sdts\conifer for DLG/SDTS data or
c:\data\sdts\big_bull for DEM/SDTS data), then click
the Extract button. This will unzip and
untar the files.
NOTE: Do not rename files extracted from the
tar file. The files in an SDTS transfer
are
referenced by name in other files of the transfer. Renaming .ddf files will break these
relationships.
4.3.2
Other tar and zip utilities
Tar and gzip for DOS, UNIX, and NT operating
systems are available in the GNU utilities from
the Free Software Foundation. Software locations for each operating system
listed below.
4.3.2.1 DOS tar and zip utilities
Copies of these can be retrieved from
ftp://ftpmcmc.er.usgs.gov/pub/sdts/software/tools/tar.exe
ftp://ftpmcmc.er.usgs.gov/pub/sdts/software/tools/gunzip.exe
These must be run in a DOS window, using the
following syntax:
to Unzip: <path>\gunzip
<filename>
to Untar: <path>\tar xvf <filename>
where <path> is the path to the
directory that contains the gunzip and tar executables.
4.3.2.2 UNIX tar and zip utilities
Copies of these can be retrieved from
ftp://ftpmcmc.er.usgs.gov/pub/sdts/software/tools/tar
ftp://ftpmcmc.er.usgs.gov/pub/sdts/software/tools/gunzip
4.3.2.3 NT tar and zip utilities
Copies of these can be retrieved from
ftp://ftpmcmc.er.usgs.gov/pub/sdts/software/tools/winnt/tar.exe
ftp://ftpmcmc.er.usgs.gov/pub/sdts/software/tools/winnt/gunzip.exe
5.
Problems Downloading Data
The availability of free SDTS data has
caused severe overloads on the GeoData server and
relatively frequent periods of down time.
Until hardware upgrades can be applied, we can only
suggest trying at "off times" of
the day.
Unfortunately, the USGS does not have the
staff to provide tutorial support for commercial
software. If you cannot access these data
through your browser, we recommend either:
- studying your software documentation for
anonymous ftp configuration procedures,
or
- using an ftp utility instead of a browser.
5.1 FTP
Different brands and versions of web
browsers implement anonymous ftp differently. The USGS
has tested a number of browsers on the ftp
site described in this paper and believes that the
data can be accessed through most browsers.
However, the default browser configurations are
not always correct for anonymous ftp access,
and in some cases changing those configurations
is somewhat difficult.
Some sites where ftp utilities can be
downloaded and purchased are:
http://www.cuteftp.com
http://www.ftpx.com
As an alternative, users of Win95 or WinNT
can ftp data using the Run function on the Start
Menu:
Type ftp://edcftp.cr.usgs.gov and select OK.
Login:
anonymous
Password:
your e-mail address in the form
name@domain
From there, make the following choices: pub/data/DEM/7.5min/B/big_bull_mountain_CO
(this
will get you to the DEM/SDTS data set we
used in our example earlier)
At this point the user is able to navigate
to the layer to be downloaded.
To change the data transfer type to binary,
type binary.
To specify which directory the data is to be
downloaded to, type lcd name of directory.
To download the data, type get name of file.
To exit, type quit.
6.
Conclusions and Points of Contact
DLG/SDTS and DEM/SDTS data are relatively
new. The design of these data could and
will be
improved for future data production. The
data are usable in their current form if proper
procedures are followed and appropriate
software is available.
For more information about SDTS, see
http://mcmcweb.er.usgs.gov/sdts. To
make
comments or ask specific questions about
SDTS or the USGS implementation of DLG/SDTS,
send mail to sdts@usgs.gov
For information about dlgv32, USGS freeware
for Windows 95 that will display DLG/SDTS data,
see
http://mcmcweb.er.usgs.gov/viewers.