Surface type: gravel vs fine_gravel vs compacted

TwoWheelsGood · 2018-03-14T17:12:31.000Z

I’m mapping what we call gravel trails in my locale (TX, US), but OSM has many different surface types. My reading of the wiki would indicate either fine_gravel or compacted. It’s kinda loose, bikes leave an impression.

Here’s some pictures from the trails in question. Any suggestions how I should tag them?

westnordost · 2018-03-15T21:20:38.000Z

I’d see the difference between fine_gravel and compacted in that the stones in fine_gravel is still loose (you know,like this) and compacted is not loose.

So, all three look compacted to me. The one in the center seems to have only loose pebbles on the very surface, but all in all it seems to be compacted.

ftrebien · 2018-03-16T13:08:44.000Z

They look more like compacted than fine_gravel to me too. Along the series compacted/fine_gravel/gravel/pebblestone/dirt/earth we’re very likely to find borderline cases, and the exact difference between compacted and fine_gravel has never been very clear.

From the OSM definition (which may be ambiguous), the differences are as follows (italicized parts are IMHO difficult to verify):

Material

fine_gravel: firm granules at the top, gravel base

compacted: mixture of large and small particles (eg. gravel and sand), built by mixing them with water (water-bound macadam) and then compressing them with a roller

Stability

fine_gravel: heavy vehicles don’t move stones, no bicycle trail marks when dry

compacted: stable and better grip than gravel (perhaps this also refers to fine_gravel?)

Shape

fine_gravel: concave, with drainage channels on the sides

compacted: no particular shape (they usually look flat to me but some sources suggest they may eventually have the same concave shape with drainage channels)

I know that compacted is resistant to weathering (rain, heavy vehicle traffic), though they may deteriorate under intense heavy vehicle traffic.

I believe both types of roads may also be colloquially called dirt roads in the US, even though dirt in OSM is considered prone to erosion.

ftrebien · 2018-03-16T13:22:07.000Z

I found this video in a Quora post that suggests that compacted roads are very dense and resistant.

Outside OSM, fine gravel is just a description of gravel with a particular granule size and the granules are usually loose (as in surface=gravel). As such it is a component of compacted preparations.