Hypsography Documentation

3.1 HYPSOGRAPHY--MAJOR CODE 020

3.1.1 General Principles

3.1.1.1 Node Attribute Codes

There are no general principles that apply to node attribute codes.

3.1.1.2 Area Attribute Codes

There are no general principles that apply to area attribute codes.

3.1.1.3 Line Attribute Codes

The elevation parameter (02N ----) is used in conjunction with all line attribute codes, with the exception of watershed divides (202 0207) and processing lines (020 0299).

Only one code from the list of line attribute codes is assigned to each line. The condition of carrying takes precedence over other characteristics; if a contour is both carrying and supplementary, it is collected as carrying only.

On the map, contour lines may be broken for elevation labels. In collecting the contours, these breaks are ignored and the contours are collected as continuous lines through the breaks. When the breaks occur along curves on the contour, care must be taken to retain contour shape relative to the adjacent contours.

In general, contours are collected exactly as they are shown on the map. There is no requirement to add or modify contour segments to improve the logical consistency of the file. However, limited additions or modifications may be made to maximize the utility and efficiency of quality control software. For example, if a contour carries on one end and is feathered on the other, it is not necessary to treat both ends one way or the other in the digital data, but you may choose to do so in order to simplify processing. Any short segments that are added or modified are not uniquely identified; they are simply assigned the appropriate contour and elevation codes.

If contours at dams, seawalls, locks, levees, etcetera, have not been scribed or have been overprinted, they are not generally connected in the digital file. However, when the path of the contour can be readily determined (for example, when a contour crosses a road at a bridge wing tick) collect the contour as a continuous line, rather than breaking it for the overprinting feature.

3.1.1.4 Single-Point Attribute Codes

The elevation parameter (02N ----) is used in conjunction with all single-point attributes.

Collection of Spot Elevations

Spot elevations values are shown in italic type on standard graphics, and with slant lettering on provisional editions.

When collecting spot elevations from graphic source, it is not always clear exactly where to collect the elevation based on its portrayal on the graphic source. The following general guidelines should be used in determining where to collect a spot elevation.

Where the spot elevation is shown by symbols 224(A), 112.41(B), 512.108(C), or 2102.10(D), digitize a degenerate line at the center of the X. Where the spot elevation value is adjacent to another feature (for example, a well, windmill, or drill holes), digitize a degenerate line at the location of the coincident feature. Where the spot elevation value is shown at the intersection of two or more linear features (for example, the intersection of two or more roads, a road and a transmission line, a road and a fence line, or two streams), digitize a degenerate line where the features intersect. Where the spot elevation is shown at a horizontal control station, digitize a degenerate line coincident with the horizontal control station. Where the spot elevation is shown on a hill or top, but no spot elevation cross is shown, digitize a degenerate line at the center of the top as defined by the top contour.

All spot elevations shown on the standard graphic are collected. Because spot elevations with suspect elevation values will generally be flagged by the processing software, they may be corrected in advance of processing if it is determined that this approach is more efficient than following up on processing software warning messages. Please note, however, that any spot elevation that agrees with the value shown on the graphic is not considered to be an error in the DLG; such suspect elevations are only to be corrected when it is more efficient to do so.

On provisional maps, elevations labeled "AT," "DB," or "DR" are not collected.

Marked overcrowding of spot elevations often exists on provisional maps, and they should not be collected any closer together than every quarter mile. If it is necessary to "thin" spot elevations shown on provisional edition maps, elevations labeled "T" are eliminated first, then elevations labeled "A" or "B," and finally unlabeled elevations.

Spot elevations are generally digitized as degenerate line elements; however, they are digitized as node elements when located on a line collected in the Hypsography category.

Elevations on bridges are encoded uniquely so they may be isolated from ground-level elevations used for Digital Elevation Model gridding or automatic contour tagging, and so that they may be symbolized correctly at time of product generation.

Type Placement for Spot Elevations

Figure 3.1-1 provides graphic examples of the preferred placement of type for spot elevations. For each situation, the placement illustrated in column 1 is most desirable, and that in column 4 is least desirable. These illustrations may be helpful in determining what location a specific spot elevation value refers to, and where to collect the degenerate line.

3.1.1.5 General Purpose Attribute Codes

There are no general purpose attribute codes.

3.1.1.6 Descriptive Attribute Codes

There are no general principles that apply to descriptive attribute codes.

3.1.1.7 Parameter Attribute Codes

There are no general principles that apply to parameter attribute codes.

---------------------------------------------------------------------------

Figure 3.1-1

Type placement preference for spot elevations

---------------------------------------------------------------------------

3.1.1.8 List of Hypsography Attribute Codes

3.1.2 Node Attribute Codes

There are no node attribute codes.

3.1.3 Area Attribute Codes

This code is described in section 3.0.6.1.

This code identifies an area where contours have been dropped due to mining activity and replaced by the disturbed surface pattern. The area beyond the national boundary is also coded as a void area, to distinguish it from the background area. The perimeter of the void area is collected as an unattributed line unless defined by a limiting contour. On topographic-bathymetric editions, void areas are also collected where features, such as channels and spoil areas, exist and bathymetric contours are not shown.

When collecting a void area where contours have been dropped and replaced by disturbed surface pattern, the edge of the pattern is used as a general guide in digitizing the perimeter of the void area. However, the perimeter of the void area must connect to the dangling ends of the dropped contours, so in some cases it may be necessary to digitize the perimeter of the void area slightly beyond the edge of the disturbed surface pattern, or within it.

3.1.4 Line Attribute Codes

This code identifies both index and intermediate contours based on the contour interval. They are shown by symbols 300, 301 (A); 132.1, 132.2 (B); 532.1, 532.2 (C); or 2302.01, 2302.02 (D). Use descriptive codes for depression (020 0611), approximate (020 0610), glacier or snowfield (020 0612) and underwater (020 0613) as needed.

This code identifies a portion of a contour at cliff embankments and similar features where multiple contours merge into a single line. The carrying contour is digitized as separate line segments. Carrying contours are given the parameter elevation codes of the highest and lowest contours joined to the nodes of the carrying contour segment. Carrying contours are shown by symbols 306(A), 132.5(B), 532.5(C), or 2302.03(D).

Any portion of a carrying contour that carries one or more depression contours is also assigned the descriptive code for depression (020 0611).

Any portion of a carrying contour that carries only approximate contours is also coded approximate (020 0610). However, if any of the contours carried by a portion of carrying contour are not approximate, then the carrying contour is not approximate.

This code identifies contours shown between intermediate contours to aid in defining topography in areas of minimal slope. Supplementary contours are shown by symbols 302, 309(A); 133.1, 133.2 (B); 533.1, 533.2(C); or 2303.01(D), or by dotted brown lines. If supplementary contours are shown on a map, there will be a note in the map collar, just below the contour interval note, that says either "Supplementary contour interval XX feet" or "Dotted lines represent XX foot contours."

Do not confuse supplementary contours with dual contour intervals. Maps covering areas with abrupt contrasts in relief may use two different basic contour intervals in different areas of the map. The contour interval note identifies maps with dual contour intervals, and a contour diagram or key, which delineates the area for which each contour interval applies, is also provided.

This code is no longer used.

This code is no longer used.

This code identifies primary, index and intermediate bathymetric contours based on the contour interval. A bathymetric contour is a line connecting points of equal water depth. Primary bathymetric contours are only collected at certain contour intervals, and are shown in black. Bathymetric contours are shown by symbols 112.87, 112.88, 141.41, 141.42 (B) or 512.147, 512.148, 541.60, 541.61 (C). This code is used in conjunction with the parameter elevation code 021 ----, 022 ----, or 024 ----. (Note that the parameter elevation codes for feet or meters below datum are not used in conjunction with this code). Also use descriptive codes for depression (020 0611), approximate (020 0610) and rise (020 0616) as needed. Do not use this code for underwater contours. See code 020 0613.

Although the sounding datum (the "0" bathymetric contour) may appear on some map separates containing bathymetric contours, it is not collected in this category. It is collected only in the Hydrography category.

This code is USED ONLY WHEN THE COLLECTION OF DEPTH CURVES HAS BEEN SPECIFICALLY AUTHORIZED AT THE REQUEST OF A COOPERATING AGENCY. Depth curves are shown by symbols 447(A) or 541.58(C). This code is used in conjunction with the parameter elevation code 021 ----, 022 ----, or 024 ----. (Note that the parameter elevation codes for feet or meters below datum are not used in conjunction with this code).

This code identifies the Continental Divide or the Tennessee Valley Divide. These features are shown by symbols 132.15(B) or 532.16(C).

This code is no longer used.

This code identifies bathymetric contours shown between intermediate contours to aid in defining water depth. Supplementary bathymetric contours are shown by symbols 512A.1, 512A.2, 512A.3, 512A.4(C). If supplementary bathymetric contours are shown on a map, it will be noted in the map collar. Use descriptive codes for depression (020 0611), approximate (020 0610), and rise (020 0616) as needed.

This code is described in section 3.0.6.3.

3.1.5 Single-Point Attribute Codes

This code is no longer used.

This code is only applied when the elevation value is preceded by the letters BR. Since these letters indicate that the elevation occurs on the bridge, the elevation should be collected directly on the bridge itself.

This code is USED ONLY WHEN THE COLLECTION OF SOUNDINGS HAS BEEN SPECIFICALLY AUTHORIZED AT THE REQUEST OF A COOPERATING AGENCY. Soundings are shown by symbol 454(A). They may be printed in either blue or black. This code is used in conjunction with the parameter elevation code 021 ----, 022 ----, or 024 ----. (Note that the parameter elevation codes for feet or meters below datum are not used in conjunction with this code).

Digitize the sounding at the center of the best fitting rectangle for the sounding value.

3.1.6 General Purpose Attribute Codes

There are no general purpose attribute codes.

3.1.7 Descriptive Attribute Codes

020 060- Descriptive attribute codes 020 0600 through 020 0609 are used to represent decimal fractions of feet or meters. They are used only in conjunction with the elevation parameter attribute codes when the original elevations are expressed to decimal fractions. The units are the same as those of the corresponding parameter code. The specific values are:

This code identifies contours in areas where accurate representation is not attainable through normal compilation procedures. Approximate contours are shown by symbols 303, 304 (A); 112.89, 132.3, 141.43 (B); or 532.3, 541.44 (C). All contours within glaciers or snow fields are also assigned this code (see code 020 0612).

The depiction of contours as approximate is uncommon; they have been used primarily in heavily forested areas in the Pacific Northwest, and occasionally in marshy areas.

This code identifies contours surrounding a basin or sink denoted by right-angle ticks (hachures) pointing inward (downslope). Depression contours are shown by symbols 307 (A); 112.90, 112A.2, 132.6, 132.7, 133.2, 141.44 (B); 512.149, 512A.3, 532.6, 532.7, 541.63 (C); or 2302.04 (D).

This code identifies contours in areas covered by glaciers or snow fields. It identifies contours within areas outlined by symbols 428, 429 (A); 141.27 (B); 541.43, 541.44 (C); or 2205.04 (D). All such contours are also coded as approximate (020 0610), regardless of how they are symbolized on the map. When a glacier or snow field is shown with form lines, as in symbols 430(A), 141.28(B), or 541.45(C), it is not collected in the Hypsography category.

This code identifies submerged contours compiled before an area was inundated by the construction of a dam. These areas are overprinted with blue or purple tint.

This code is no longer used.

This code is no longer used. Portions of contours along which fill ticks are shown are not uniquely identified.

This code identifies contours surrounding a rise inside a depression, shown by right angle ticks, pointing downslope, as in symbols 112.91, 112A.3, 141.45 (B); or 512.151, 512A.4, 541.64 (C).

This code is used only in conjunction with bathymetric contours (020 0205 and 020 0210).

3.1.8 Parameter Attribute Codes

This code is no longer used.

This parameter is used to encode the elevation value associated with a contour or spot elevation. The digitizer enters a value in place of the "N" in the major code as follows:

The elevation value is then entered into the minor code, flush right. (For elevations greater than 9999 feet, only the final four digits are encoded in the minor code.)

Examples: 12,400 feet is coded as 021 2400

Elevations exceeding 19,999 feet must be expressed in meters. Mt. McKinley, Alaska, is the only point within United States boundaries that falls in this category.

To express elevations to decimal feet or meters, use the above parameter codes in conjunction with descriptive attribute codes 020 0600 through 020 0609.

Negative contour elevations are found on maps of only a few areas of the United States, such as New Orleans or Death Valley.

In areas where contour feathering occurs, elevations for the feathered segments can generally be determined by referring to the compilation specifications for feathered areas. These specifications state that the last contour segment dropped in a constricted area is the first one to begin again as soon as space is available. The compilation specifications also state that when the space between index contours limits the depiction of intermediate contours, the priority for portrayal is as follows: the highest intermediate, the lowest, the second highest, the second lowest, and so on.

This code is no longer used.

This code is no longer used.

For additional information regarding this Web page, contact Deb Southworth Green, in the Division of Information Resources and Technology Management, at Deb_Green@fws.gov

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

Last Modified January 03, 2001 10:33 AM