December 8, 2017
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Since acquiring an improved GPS, I have been surveying highways, train routes, bike paths and hiking trails, merely by carrying the GPS while driving, riding or walking the route. The GPS is set to take a latitude and longitude reading at intervals of 0.1 miles for highways and 0.02 miles for trails, which is adequate for most mapping applications. For more recent surveys, intervals of 0.02 miles are used in all cases. Some bike and hiking paths were surveyed manually, with appropriately spaced waypoints. In some cases, additional points were inserted into highway tracks near tight curves.
On each trip, I recorded points of interest, particularly the beginning and end of the route and stations (for railroads) or interchanges and intersections (for highways), as waypoints. These are embedded into the tracks at the proper locations with suitable comments.
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. Since freeway interchanges can be rather large, the coordinates of interchanges are even less accurate.
After much processing, the results were packed into simple database tables in .DBF (dBase) format. Tables in this format can be imported into most database applications. The fields are as follows:
name type width decimal description --------- --------- ------ ------- ----------------------------------------- SERIAL Numeric 3 or 4 0 record number (1 is first) LATITUDE Numeric 11 6 latitude in degrees (north is positive) LONGITUDE Numeric 11 6 longitude in degrees (east is positive) ELEVATION Numeric 5 0 elevation in feet DISTANCE Numeric 6 2 distance in miles from beginning of track COMMENT Character 64 comment for embedded waypoint
For each track, a summary file was prepared giving the serial numbers, distances and comments for each embedded waypoint.
The two files for each track have the same name. The database file has extension .DBF and the summary file has extension .TXT. The names are limited to eight characters to make them accessible by old software, and their mnemonic value is somewhat limited.
Generally, each table is in south-to-north or west-to-east order, even if the route was driven or ridden in the opposite direction. There are two exceptions.One exception is California Highway 54, whose eastbound and westbound lanes between I-5 and I-805 are separated by the Sweetwater River. The westbound lanes in this area were surveyed separately. However, the points are listed in west-to-east order even in this case. Highway I-8 has some widely separated eastbound and westbound lanes in the mountains, so the westbound lanes are listed separately east of E. Willows Rd. A table for a hiking trail generally starts at the trailhead.
County highways are incompletely signed in some places. They often bear several street names, and it is not always clear where the names change. In some cases, it is not even clear where a county highway begins or ends.
California Highway 188 was surveyed in both directions, and then the points were merged.
Points listed as "US-MEXICO BORDER" are actually some distance north of the border.
The list of tracks was made into a database. It can be accessed as TTRACKS.DBF and loaded into a database or spreadsheet program. However, an HTML version ttracks.htm may be easier to use, since it has links to the individual tracks and also to a summary showing only the commented points of interest.
The fields in TTRACKS.DBF are as follows:
name type width decimal description --------- --------- ------ ------- ----------------------------------------- NAME Character 50 name of track LOCATION Character 50 (starting) location FILE Character 8 file name for track and summary TYPE Numeric 1 type of track: 1 railroad 2 interstate highway 3 California state highway 4 San Diego county highway 5 major named road 6 minor named road 7 bike path (paved) 8 trail (unpaved) LENGTH Numeric 6 2 length of track in miles POINTS Numeric 4 number of points in track YEAR Numeric 4 year of most recent survey COMMENT Character 50 comment
Each track can be accessed individually as DBF/ffffffff.DBF and its summary at TXT/ffffffff.TXT, where "ffffffff" is the file name in the FILE field in the table TTRACKS.DBF (with trailing blanks removed). The tracks and summaries can be downloaded en masse in the compressed files DBF/archive.zip and TXT/archive.zip, respectively.
The term "trail" includes equestrian and mountain biking trails and dirt roads that are not open to motor vehicle use (except for emergency and maintenance vehicles).
Philip J. Erdelsky email@example.com