Augmenting MapViewer Boundary Data with USGS DLGs

Introduction

MapViewer 5 comes with many boundary data files, such as continents, countries of the world, US states and counties, etc. However, it is common for people to supplement these boundaries with data they create themselves or acquire from other sources. Since MapViewer supports several standard geographic file formats, there are many possible sources for additional information.

One source of data in the United States is the U.S. Geological Survey (USGS). Several different types of files are available through their data download page.  This article takes a look specifically at the USGS Digital Line Graph (DLG).

Digital Line Graphs (DLGs)

DLGs are digital vector representations of cartographic information derived from USGS maps and related sources. They are available at three different scales:

• Large-scale (1:24,000), which correspond to the 7.5 minute topographic quadrangle maps.
• Intermediate-scale (1:100,000), which are derived from the 30 minute by 60 minute quadrangle maps.
• Small-scale (1:2,000,000), which are derived from the USGS sectional maps from the U.S. National Atlas.

Which features are represented in the DLG depend on the scale, but can include:

• Boundaries
• Transportation
• Public Land Survey System (PLSS)
• Hydrography
• Hpysography
• Survey control and markers
• Man-made features
• Vegetative and non-vegetative land cover

The rest of this article will explore making a MapViewer map of the roads in a single US state (Indiana) from the transportation features in a small-scale DLG.

Downloading the DLG

Begin by going to the USGS Data Download page. Buttons across the top of this page take you to the different data sets that are available.

A number of different data sets, at different scales, are available.

We want the small-scale DLG, so click on the 1:2M DLG button.

Using either the FTP via State or FTP via Graphics links, navigate to the state of interest. Choosing the state reveals a list of the files that are available for download, such as:

Five sets of DLG files are available to download for Indiana.

These files contain the boundaries, hydrography, man-made features, PLSS, and transportation features for Indiana. Roads are contained in the transportation group, so click on IN.trans.sdts.tar.gz to download this file. Save it to a folder on your system.

Unpacking the DLG

Note that the downloaded file ends in ".tar.gz". These are archiving and compression formats commonly used on UNIX systems to pack multiple files into one compressed archive, similar to a ZIP file on a PC. Fortunately, most PC ZIP programs, such as WinZip understand these formats. However, if you are using WinZip, there is an important setting that may need to be changed before unpacking the DLG.

Start WinZip and go to Options | Configuration on the main menu.

Check the WinZip configuration options.

Next, go to the Miscellaneous tab in the Configuration dialog. Look for the TAR file smart CR/LF conversion option and make sure it is NOT checked. If it is checked, then uncheck it and click OK.

Uncheck the TAR file smart CR/LF conversion option in WinZip.

On UNIX systems, the end-of-line in a text file is indicated by a single line-feed (LF) character. Windows uses a carriage-return / line-feed pair (CR/LF) instead. The "smart" option in WinZip converts each LF character it sees into a CR/LF pair. This is fine for text files, but not for binary data, like the DLG.

After checking the WinZip option setting, use it or another unzipping program to unpack the files from the DLG. When you do this, you will get a number of .DDF files. In the case of this Indiana transportation DLG, there are 35 .DDF files, all starting with "INTR". The information in the DLG is split up into these multiple files - all of them are needed.

Including the DLG road information in a MapViewer map

Now that the DLG has been downloaded and unpacked, we're ready to make a map of the roads in Indiana. (Incidently, Indiana is known as the "Crossroads of America".)

Perform the following steps:

1. Start MapViewer and go to Map | Base Map on the main menu.
2. In the Import Boundary File dialog, make sure the Append image and Specify import options boxes are checked, select any one of the 35 INTR*.DDF files, and click the Open button.
3. In the STDS-TVP Import Options dialog, choose No Nodes, All Lines, and No Areas in the Objects group.
4. Also, in the Selection Criteria group, choose LE01 from the By Module dropdown list. The choices in this list are different layers in the DLG. Layers starting with "LE" contain line objects. LE01 is the layer containing the roads. The STDS-TVP Import Options dialog should now look like:
    
   
   

   Import all lines from module LE01.

5. Click OK.
6. In the Import Options dialog, you can choose which data fields from the DLG to map to the MapViewer data fields (PID, SID, Attribute 1, and Attribute 2). Reasonable choices might be the ROUTE_NUMBER and ROUTE_TYPE. The other data fields in this DLG are largely blank.
    
   
   

   Choose the mapping between DLG and MapViewer data fields.

7. Click OK to create the map.
    
   
   

   The roads of Indiana.

If you have any questions about MapViewer or this article, please contact us at mapviewersupport@goldensoftware.com.

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