Dlg files gis

Sometimes the coverage will have arc intersections and will need to be cleaned using the Clean tool. The feature attribute table NAT is automatically created and does not require an additional build for nodes. The Output Coverage may require editing before polygons or lines can be built and feature attribute tables created.

For example, checks should be made on the output coverage to ensure that label points occur within their polygons, arcs match at nodes, polygons close, arcs do not cross, and so on. ACODE and output coverage. The CODE files, output coverage. PCODE, hold line attribute codes and polygon attribute codes.

There is no corresponding CODE file for node attributes. The User-IDs and attribute codes for node N records are stored directly in the output coverage. NAT feature attribute table. An Output Point Coverage. The Cover-ID is each feature's unique identifier. If no value appears for a particular code, it will be set to DLG header records may contain parameters of a transformation that are used to convert the internal file coordinates to the ground coordinate system.

Import From DLG will automatically apply any transformation parameters found in the header records to the feature coordinates and control points in addition to any specified shift. The header records in the DLG file provide information used to determine the tic locations of the output coverages.

If the fields used to store control point information are blank, Import From DLG will generate tics for the output coverages. DLG files usually provide four control points representing the four corners of the map area in the same map coordinate system used to store geographic features.

Any transformation or x,y shift applied to the feature coordinates will apply to the control points as well. Categories are listed in DLG header records. The coordinate precision of the output coverage is determined by the current creation rule. If the precision setting has not yet been established during the current session, then the creation rule will be Single.

Coordinate values in DLG files have a format definition of F Not all DLG layers are available for all areas at all three scales. Coverage is complete at ,, At the intermediate scale, , 30 minutes by 60 minutes , all hydrography and transportation files are available for the entire U. At , 7. The files are in the public domain, and can be used for any purpose without restriction.

In one sense, DLGs are as much "legacy" data as the out-of-date topographic maps from which they were produced. DLG hypsography data have not been included in the National Map, however. Hypsography refers to the measurement and depiction of the terrain surface, specifically with contour lines.

Several different methods have been used to produce DLG hypsography layers, including:. The preferred method is to manually digitize contour lines in vector mode, then to key-enter the corresponding elevation attribute data.

The instructions below assume that you have already installed the software on your computer. If you have not done so, return to the download and installation instructions presented earlier in the Chapter 6, section 6 Try This! First you'll download a sample DLG file. In a following activity you'll have a chance to find and download DLG data for your area. Skip to main content. Table 7. Figure 7. Transportation features are arbitrarily colored red, hydrography blue, and hypsography brown.

The square symbols are nodes and the triangles represent polygon centroids. Notice that the line feature is attributed with a unique Element ID code LE01, and an elevation feet. Try This! Next, Download the DLG. The ZIP archive is 1. Now, decompress the archive into a directory on your hard disk. Open the archive DLG.