BOARD01965

• Board Meeting Date: 3/22/2005
• Description: Flood Section - Presentation of the CWCB's Draft Rules and Regulations for Regulatory Floodplains in Colorado
• Board Meetings - Doc Type: Memo

GUidelines and Specifications for' Flood Ha:m'd Mapping Partners [Ap,'if 2003J

A.1

Appendix A
Guidance for Aerial Mapping and Surveying
Introduction

[February 2002]

This Appendix presents Federal Emergency Management Agency (FEMA) aerial mapping and
surveying guidelines and specifications that have been established to specify the quality of the
spatial data products to be produced, including work maps and base maps used in the production of
Flood Insurance Rate Maps (FIRMs), Digital Flood Insurance Rate Maps (DFIRMs), and
DFIRM-Digital Line Graphs (DFIRM-DLGs). The term "FIRM" is used generically hereinafter to
specify this "family" ofFEMA spatial products.

This Appendix also includes guidance for ground surveys of control points, cross sections, and
hydraulic structures, and for topographic mapping using photogrammetry, Light Detection and
Ranging (LIDAR), or other airborne remote-sensing technologies consistent with FEMA and
industry standards.

A.1.1

Base Maps

[February 2002]

A FIRM base map is a planimetric map, in digital or hardcopy format, showing the georeferenced
horizontal location of mapped features, without depiction of elevation data such as contour lines.
Georeferencing means that the map depicts the spherical earth projected as a plane map, normally
with Universal Transverse Mercator (UTM) or State Plane coordinates, with or without tick marks
or lines that depict parallels (lines of equal latitude) or meridians (lines of equal longitude). Base
maps may be categorized as either vector maps or raster image maps, depending on how they are
produced.

Vector maps result from linear features (e.g., roads, railroads, streams) digitized as single-line
centerlines or, alternatively, as dual-lines showing the outer extremities oflinear features (e.g., left
and right banks of streams, curb lines on both sides of streets). Vector maps are digitized in such a
way that a Geographic Information System (GIS) can automatically derive intelligence from the
vector features and perform analyses (e.g., adjacency analyses, proximity analyses, and
connectivity analyses).

Raster image maps result from digital scanning of paper maps, map negatives, aerial photographs,
and orthorectification of those images so that they are accurately georeferenced with distortions
removed. Raster image maps rely on human interpretation of scanned or imaged features to derive
intelligence therefrom. The most common form of raster image map is the digital orthophoto,
especially the standard Digital Orthophoto Quadrangle (DOQ) produced by the U.S. Geological
Survey (USGS).

A-I

Section A.l