While I’ve been working on BLM Ground Transportation Linear Features (i.e. highways) in Imperial County, I took a small diversion to put in the BLM Off-Highway Vehicle Areas in California. Four of the major BLM OHV areas are in Imperial County, so it was relevant. These boundaries are important because many of the OHV areas are “open,” allowing cross-country travel off of designated roads and trails.

I’ve been working with the BLM CA Off Highway Vehicle Designations data set, which has 31 OHV areas in California and one OHV area from Nevada that slipped in because it’s managed by a BLM field office in California.

As I started adding the OHV areas, I noticed that almost all of these areas have never been mapped. Some of these areas are notable institutions in the off-road community, like Imperial Dunes (aka Glamis) and Johnson Valley (home of King of the Hammers). So adding these areas is a significant contribution to the map.

Tagging these areas is a little bit of a challenge. After some discussion with Minh Nguyen, I settled on https://wiki.openstreetmap.org/wiki/Tag:landuse=recreation_ground and https://wiki.openstreetmap.org/wiki/Tag:leisure=offroad_driving to tag all the OHV areas. The recreation_ground tag is a slightly odd fit but it seems close enough to be appropriate. And some renderers have an idea what to do with it.

Some of the OHV areas only permit vehicles on designated routes. That’s no problem because the access tags go on highway features and the OHV area doesn’t need any additional tagging. But many OHV areas permit open cross-country riding, so tagging vehicle access is an issue for these areas. I settled on adding motor_vehicle and ohv access tags directly to the areas, with values like yes for unrestricted access, permit where vehicles must have a pass, and permissive for the shared-use area of Johnson Valley which is periodically closed for military use (but not on a predetermined schedule).

The motor_vehicle tag implies the same access conditions for motorcycles, and the ohv tag includes both buggies and ATVs, so the OHV areas don’t need specific motorcycle or atv tags.

The El Mirage OHV Area is open to ultra-light aircraft, gyrocopters, parasails, and full-sized aircrafts. So it gets an https://wiki.openstreetmap.org/wiki/Tag:aeroway=yes tag to cover all of the above!

Since the OHV areas are administrative boundaries, they sometimes share alignment with other boundaries. In cases where it was clear that the boundary locations were (nearly) identical, I used multipolygons to share ways between the boundaries. But in a lot of cases where the map has similar boundaries established by different agencies, the boundaries really don’t line up and there’s no clear way to resolve the discrepancies. In those cases, I left the boundaries to overlap and cross. Maybe someday there will be a reliable data source to resolve those inconsistencies.

In the end, there was one OHV area that I left off the map. It wasn’t clear how the South Spit area near Eureka is meant to line up with the terrain or existing boundaries. There didn’t seem to be much OHV activity present in aerial imagery. And I didn’t find any additional explanation on the BLM web site. So I left that for someone who might have more insight.

Putting the OHV areas on the map is also going to help me finish up adding the BLM routes in Imperial County. The Imperial Dunes OHV Area is the major spot I still have to work on. The OHV area has a central open riding area surrounded by not quite contiguous areas where riding is restricted to established trails. Having those boundaries is going to make it easier to get the access conditions on the trails right!