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June 17, 2020

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This section is devoted to surveys of boundaries of and within San Diego County. So far, only San Diego County is included, but more will be added as they are developed.

In a few places, county and city boundaries are clearly marked and publicly accessible, usually where a boundary crosses a highway. But most boundaries are marked only on maps. To avoid copyright infringements, I have used USGS topographic maps, which are in the public domain.

Each boundary is represented as a broken line connecting a number of points. Each point is located by a single record in a database table in dBase III+ format, with extension .DBF. Such a table can be readily imported into most spreadsheet programs and database management systems. The fields are as follows:

name       type       width   decimal  description
---------  ---------  ------  -------  -----------------------------------------
SERIAL     Numeric      4        0     record number (1 is first)
QUADRANGLE Character   30              USGS 7.5-minute quadrangle
LATITUDE   Numeric     11        6     latitude in degrees (north is positive)
LONGITUDE  Numeric     11        6     longitude in degrees (east is positive)
DISTANCE   Numeric      6        2     distance in miles from beginning of line
COMMENT    Character   64              comment

Latitude and longitude are given to the nearest 0.000001 degree, which is less than one foot, but the measurements were obviously not that accurate. Most are within 50 feet of the true coordinates. However, some discrepancies of as much as 0.1 mile have been found between mapped and signed locations, especially in wilderness areas.

The serial number can be used to order the table when it is imported into a database management system such as SQL which does not provide for record numbers.

Each boundary is a closed broken line, ordered in a clockwise fashion as seen from above. This is a true representation for most boundaries, which were obviously defined and laid out in this manner, but it is only approximate for boundaries defined by natural features, such as the coastline. Since the boundary is closed, the first and last records are identical.

The only surveyed boundary currently posted is that of San Diego County. The database file is SDCOUNTY.DBF, and a text summary is SDCOUNTY.TXT

Philip J. Erdelsky