FLOOD09505

• County: Statewide
• Basin: Statewide
• Title: Standards for Digital Flood Insurance Rate Maps
• Date: 10/1/1993
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

GENERAL

The Federal Emergency Management Agency (FEMA) is collecting and distributing
digi tal thematic data pertaining to flood hazard identification and flood
insurance. The standards specified in this document pertain to the collection,
processing and revision of Digital Line Graph (DLG) data intended for
distribution by FEMA.

These standards are intended to facilitate the interchange and use of DLG data,
DLG collection and processing systems must produce data that are compatible with
other production systems not only within the Federal sector but also within other
government and private sector organizations, Due to rapidly changing
technologies in the mapping industries, these DLG standards cover a broad range
of collection and processing systems, It is not the intent of this standard to
inhibit usage of any procedure, but to set common standards which will allow data
to be acceptable for entry into many different production systems. The basic
applications of DLG data are to support automation of cartographic processes and
automated spatial data analysis.

The DLG file structure is designed to accommodate all categories of spatial data
represented on a conventional map. Node, line. and area data types are accepted.
Thl! attribute coding scheme is designed to accommodate basic thematic data
categories such as political, map panel, hydrographic, and flood hazard zone
features.

Data Sources

Digital Line Graph data are usually derived by digitizing map features as line
graph elements from cartographic source materials. The map name. community name,
scale, date, and projection of the source materials is contained in the Metadata
file. '

Data Content

The DLG files derived from the Flood Insurance Rate Maps (FIRMs) contain selected
categories of thematic data in digital form; these data categories do not
necessarily correspond to the traditional feature separates associated with the
maps.

The following categories are valid for DLG files published by FEMA:

.

Political Areas
subdivisions, e.g.

This
city,

category of data
county. state.

consists of

political

.

Map Panel Areas
panelling schema.

This category of data consists of FEMA's map

. FEMA Hydrography - This category of data consists of
water control structures and surface water.

10/93

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