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Elevation-Derived Hydrography READ Rules: Ice Mass

A ice mass is a field of ice formed in regions of perennial frost.

Attribute/Attribute Value

Each feature requires domain codes to be entered into the attribute table for the feature class (Elevation-Derived Hydrography Feature type description, associated geometry, and use classification table in the Elevation-Derived Hydrography Data Acquisition Specifications 2023 revision A2). See “Field Definitions and Domain Values for Attributes” section for more information on Elevation-Derived Hydrography code definitions.


The limit of ice mass is the extent of ice or snow.

Representation Rules

When delineating a feature, it must be created with the appropriate geometry, either point, line, or polygon, which is determined by the size of the feature or the length along different axes of the feature (table 9).

Special conditions: none.

Table 9. Ice Mass Representation Rules.

Kind of feature object                  Area Shortest Axis Longest Axis
0-dimensional (point) -- -- --
1-dimensional (line) -- -- --
2-dimensional (polygon) greater than 0 -- --


Data Extraction

Capture Conditions

If ice mass is greater than or equal to 1 acre (or 4,000 square meters),

then capture.

Z-values (elevation values at a particular location) are measured at the boundary of the feature.

Attribute Information

FClass 9— Nonhydrography feature.

FCode 37800—Ice mass (a field of ice formed in regions of perennial frost).

EClass 0— Not used for elevation derivative.

Source Interpretation Guidelines

If glaciers are contiguous, then the dividing line is the approximate line of divergence or confluence, as determined by the topography of the ice masses, or by the changes in color or texture, or both.



Imagery and a map depicting ice mass features.
Mendenhall Glacier in Alaska is shown as an example of an ice mass feature. Source data are from the National Hydrography Dataset (U.S. Geological Survey, 2020), which is used to provide examples of hydrographic feature types but may not have the same density and other characteristics of elevation-derived hydrography.