Service Description: Postmiles is used to display postmile locations on a digital map display, or to query for the purposes of finding a specific location reference by county, route, and postmile. Postmiles are coded with the district, county, route, postmile prefix (if any), postmile, and postmile suffix (if any). The source of data is the Caltrans TSN (Transportation System Network) database.
Two additional fields - PMInterval and AlignCode - should be understood by the user for effective use of this data set (refer to the Entity and Attribute Information section of this metadata).
PMInterval indicates the interval on which the postmile falls: 0.001, 0.01, 0.1, 1, 5, or 10. This field is handy for drawing a subset of postmiles at desired intervals, for example this Definition Query will tell ArcMap to draw postmiles only at 1 mile intervals: "PMInterval" >= 1 Though the vast majority of postmiles fall on a 0.1 (tenth mile) or larger intervals, postmiles are included that fall on a smaller interval. Examples are the beginning or end of a route or county, or at an equation point. These postmiles can be identified through use of the "HwySegment" field that contains codes of "Begin County", "Begin Segment", "Mid Segment", "End Segment", and "End County". Begins and ends of routes are coded "Begin County" and "End County". A Definition Query that would tell ArcMap to draw postmiles only at 1 mile intervals or the begin of county would be: "PMInterval" >= 1 OR "HwySegment" = 'Begin County'
AlignCode indicates if the postmile is on a Right alignment, Left alignment, Right Side of an independent alignment, or Left Side of an independent alignment. Where TSN considers most state highways to have just a centerline, the underlying linework that the postmiles are based upon has a line for each direction. On undivided highways the right and left lines are identical. On divided highways the right and left are separated, but TSN treats the segment as a single centerline. In the last case where highways are not only divided but also have...
Service ItemId: b610b9b7ab3c4e008604d58801cc5d14
Has Versioned Data: false
Max Record Count: 2000
Supported query Formats: JSON
Supports applyEdits with GlobalIds: False
Supports Shared Templates: True
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Description: Postmiles are valid postmile points at 0.1 (1/10th) mile intervals, based on the Caltrans Linear Referencing System. Exceptions that are included are the beginning and ends of routes (and other situations) that don't necessarily begin or end on the even 0.1 mile interval. This geometry is based upon the extraction from TSN on 8 June 2025. . Route geometry updates based upon this extraction include routes 3, 36, 38, 49, 89, 139, 174, and 221. All updates received an update date of 6/8/2025 except for route 221 which received a date of 7/1/2025.
California Department of Transportation (Caltrans)
Spatial Reference: 4326 (4326)
Initial Extent:
XMin: -122.265805846134
YMin: 38.2468572865045
XMax: -121.4478002662
YMax: 38.4363659105949
Spatial Reference: 4326 (4326)
Full Extent:
XMin: -122.372523295113
YMin: 38.1309289115676
XMax: -121.863346633451
YMax: 38.4423984175917
Spatial Reference: 4326 (4326)
Units: esriDecimalDegrees
Child Resources:
Info
SharedTemplates
Supported Operations:
Query
ConvertFormat
Get Estimates