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:

-Shoreline

-Hydrography

-Latitude/Longitude graticule

-County boundaries

-Coastal Zone Boundary

-Railroads

-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:

-Historical shoreline

-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.