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Elevation-Derived Hydrography Data Acquisition Specifications: Attribute Table Structure Requirements

By NGP Standards and Specifications

Elevation-Derived Hydrography Data Acquisition Specifications

Attribute Table Structure Requirements

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Attribute Table Structure

 

Attribute Table Structure

The structure of the attribute tables is described in table 1, table 2, and table 3. An important component of the elevation-derived hydrography features is that they have three-dimensional (3D) geometry. Each feature type must be z-enabled, with z-values assigned to each point, vertex, and node. The feature classes (pointZ, polylineZ, and polygonZ) are 3D geometry. Each domain is described in table 4, table 5, table 6, table 7, and table 8.

  • Feature class (FClass)—A short one-digit integer code describing the hydrographic use of a feature.

    • A 1 is used when a feature is collected to meet the elevation-derived hydrography acquisition specifications. An example of features with an FClass = 1 include a point feature defined as a sink. An example of a line feature with an FClass = 1 is a stream that is too narrow to be represented as a polygon. An example of a polygon feature with an FClass = 1 is a wide river, or a lake/pond.

    • A 2 is used when a feature is outside of the collection criteria. An example is when the features add too much complexity, will not be used for network connectivity, or are outside of the 3D Hydrography Program (3DHP) collection requirements.

    • A 9 is used when a feature is a nonhydrography feature is outside of the 3DHP collection requirements. A line representing a levee, or a dam is an example of a feature that may be useful for elevation processing.

  • Feature class for elevation (EClass)—A short integer one-digit code describing the elevation use of a feature.

    • A 0 is used when the feature is not used for elevation derivative.

    • An 11 is used when the polygon derived from the breaklines used for hydroflattening the elevation surface (3D polygon).

    • A 12 is used when the polygon corresponds to a hydroflattened surface, but breakline is either not available, or not horizontally or vertically aligned appropriately with the DEM surface. For use in Alaska or where breaklines do not meet cartographic or horizontal requirements.

    • A 13 is used when the polygon was created without using elevation breakline and the surface of the waterbody is not hydroflattened in the source DEM.

    • A 2 is used for linear hydrographic features that follow the elevation surface. This is the default value.

    • A 3 is used when linear features are below ground level, examples include connectors through dams, culvert connectors, and terrain breach connectors. It is also used for hydro-enforcement.

  • FCode—A long integer field containing a coded value. Most of the FCodes are equivalent to the NHD FCode value, which is a five-digit integer code representing various hydrologic feature types. For instance, a lake/pond has an FCode of 39000, and a stream/river has an FCode of 46000. The codes that do not have a corresponding NHD code are included to differentiate features that may be useful in describing limitations in the elevation dataset, potentially affecting hydrography and elevation derivatives.

  • Desc—A 250-character free-text field with a text description of FCode, or it can be used for user-defined features not included in the domain list. Not required.

  • Source—A 128-character free-text field with a text description of the elevation source data used for deriving the hydrography. Lidar-source data will include collection name, date, and quality level.

  • Method—A 250-character free-text field with a text description of the method used for deriving the hydrography. For instance, software or models could be listed, or digitizing techniques, if used. Ancillary datasets could be noted here.

  • User-defined code (UserCode)—A 25-character free- text field with a code designated by the acquisition entity to identify features collected outside the scope of features described in this specification document. It is intended to be used as a key to join tables with attributes outside of this specification. Not required.

  • Comments—A 250-character free-text field for user comments. Not required.

  • UniqueID—A 50-character free-text field that stores a Unique Identifier for each feature in the dataset. The UniqueID is intended to be stable throughout multiple deliveries of a dataset within a project area. The Unique ID field is meant to be populated by the contractor prior to delivery of data to the USGS.  Unique IDs allow communication with contractors by providing a tracking system for individual features.

  • FlowClass— A short integer one-digit code used in the line feature class that describes whether a feature's flow direction can be determined. In most cases, features will be digitized in the direction of flow and will flow downslope (Flow = 1). In very flat, wetland or tidal areas, it is often impossible to determine the direction of flow (Flow = 0).  Water may occasionally flow uphill, such as when a pump is used or, in rare cases, in natural situations. A segment’s z-values may flow in an upslope direction in cases where water enters a depression on the landscape and must rise in order to exit the depression. When flow is known to initiate from a lower elevation and discharge to a higher elevation, Flow = 2.   

  • Limitation— A short integer one-digit code that indicates whether the source elevation contained limitations that create issues meeting vertical or horizontal requirements for the hydrography feature.