U.S. Fish and Wildlife Service

Notes on Hypsography data, SDTS format

The hypsography line data converts quite smoothly to a shapefile via DLG format. The match between attributes converted this way and converted in Arc/Info, and then comparing both to the original DLG files, is good.  The polygon data, however, does have some differences.  Polygons that are not completely closed within the quad being converted are not assigned an attribute value in Arc/Info (using the AML SDTS2COV).  In Arcview they are.  The outlines of the polygons are the same, and the elevation values for polygons that are assigned values by both methods are the same; the problem is one of differing approaches rather than conflicting attribute values.

The feature attribute primary module for hypsography contains the letters AHPF in the name. In some cases there may be a coincident attribute primary module with the letters ACOI in the name. This coindcidence module is less common in hypsography than roads, public land survey or other data layers with more regular features. There is also usually a module with the letters AHPT or AHPR containing elevation values in feet or meters (occassionally there may be both). 

The SDTS2DLG program creates a DLG and a DLA file when run. Running the DLGBLD program links the records within the DLG file. The DLA file contains information about the topoplogy of the data (line, node, etc) and functions as a link between the attribute information and the actual topology features. The first column indicates Area, Point, Line or Node. The second links to a record id in the attribute file (RCID), while the next column links to an attribute id in the attribute file (ATID and RCID). The fourth column matches the minor code in the DLG file, and the last points to the file where the attribute will be found (most often the feature attribute primary module).

The following is sample data from the hypsography DLA file.

A, 606, 606, 605 , PC01
A, 607, 607, 606 , PC01
P, 1, 1, 607 , AHPF
P, 1, 1, 608 , AHPT
P, 4, 4, 613 , AHPF
P, 4, 4, 614 , AHPT
P, 4, 1, 615 , ACOI
L, 61, 61, 737 , AHPF
L, 61, 61, 738 , AHPT
L, 62, 62, 739 , AHPF

The PCATDUMP program creates an equivalent format file for the polygon data; unfortunately it does not seem to work for the Hypsography data. To get around this problem, the area (polygon) records were extracted from the hypsography DLA file after it was converted to a DBF format and used in the polygon relates.  See the notes on this in the DBF conversion section below.

The ATTR2DAT program creates a file from the feature primary attribute module. This file contains attribute information in a useable format. The file is bascially an ascii delimited text file, although it is created with a DAT extension. For the hypsography line data, only the first two columns are used.

The following is sample data from the hypsography DAT file (avhpahpf.dat), directly after conversion:

12,0200300, , , , , , , , , , ,
13,0200300, , , , , , , , , , ,
14,0200301, , , , , , , ,17, , ,
15,0200301, , , , , , , ,17, , ,
16,0200300, , , , , , , , , , ,
17,0200301, , , , , , , ,17, , ,
18,0200300, , , , , , , , , , ,
19,0200300, , , , , , , , , , ,
20,0200300, , , , , , , , , , ,
21,0200300, , , , , , , , , , ,
22,0200301, , , , , , , ,18, , ,

The data below is a sample from the related elevation file (hp01ahpt.ddf) converted by running the ATTR2DAT program a second time. Note: the SDTS documentation indicates that the file hp01ahpt.ddf contains elevation in meters in one place and in feet in another location.  The measurements below are actually elevation in feet.  This file was named avhpahpt.dat.

1, 5324.00
2, 5319.00
3, 5476.00
4, 5572.00
5, 5560.00

ArcView Conversion to DBF File Notes:

To convert all .dat and .dla hypsography files to .dbf files, the dlgattin.ave program was run twice.  The same dlg file was referenced both times, but the AHPT string was used one time and the AHPF string the other.  Error references to an out of range index were recieved both times, but the dbf files created were good. 

To create the replacement file for the PCATDUMP program, the file avhpdla.dbf zxhad a subset selected, where the field feature = A (area).  The selected items were saved to a new file called avhppol.dbf.  This file was then used in the Area Data directions under the general ArcView Shapefile Conversion Steps.  The only differences were the field names (recid vs recidpol and attid vs attidpol), and the fact that you do not usually need a lookup table for hypsography - just the elevation values.

For additional information regarding this Web page, contact Chris Lett, in the Division of Information Resources and Technology Management, at Chris_Lett@fws.gov

Return to the GIS Activities Home Page
Visit the U.S. Fish and Wildlife Service Home Page

Keywords=GIS, data, metadata, steering, standards
Last Modified January 04, 2001 07:30 AM