The historic maps show the earliest available record of the wetland
perimeter. The 42 wetlands are displayed on 39 USGS 7.5 minute
quadrangles. Each map shows the historical wetland extent as well
as the year in which the wetlands were surveyed. The methodology
used to produce these maps is described below.
Creating the Base Map
The thematic historical wetland layer was added to a digital base
map. To complete the base map information for this set of maps,
the following data layers were digitized from USGS 7.5' quadrangles:
-Coastal Zone Boundary
-NGS control points and benchmarks
-Place names and other text labels
-Scale of capture 1:24,000
Capturing the Wetland Data
The historical wetland extent was developed from U.S. Coast and
Geodetic Survey (currently NGS) Topographic Maps, commonly referred
to as "T-sheets," completed between 1851 to 1893. This
information was available in two formats, the first being paper
reproductions of the original T-sheets at the original scale (usually
1:10,000) and the second being mylar copies of USGS 7.5' quadrangles
onto which the wetland boundaries had been transferred by CA Dept.
of Navigation and Ocean Development (currently Dept. of Boating
and Waterways). To minimize the amount of error introduced by
DNOD's boundary transfer, it was decided that the historical wetland
boundaries should be digitized directly from the paper USC&GS
T-sheets whenever possible.
In order to facilitate registration of the historical wetland
extent with the USGS base map, the 1927 North American Datum (NAD)
was used for control. The 1927 NAD was available for all but three
T-sheets utilized in the inventory. For these map sheets it was
generated from adjacent T-sheets.
The following information was digitized from the historic maps:
-Landward boundary of wetland symbols, including marsh, salt ponds and alkali flats
-T-sheet number and year of survey
-Scales of capture 1:10,000, 1:20,000, and 1:24,000
Platform: IBM Compatible PC - DOS/Windows
Software: AutoCad r12, ArcCAD r11, ArcView v2.1
Hardware: NETIS 90 mhz Pentium PCI: 32 MB RAM, 2 GB disk space, C-ROM, Ext. DAT (4 GB uncompressed capacity)
Copies of the final set of 39 maps (plus an index map) are available for approximately $70. For ordering information, contact the Technical Services Division of the California Coastal Commission.
Copyright © 2007 State of California