James Umbanhowar <jumba...@gmail.com> wrote: > Something else to consider is that even though there is a perimeter for > a fire, there can be highly variable impacts on the landcover within > the perimeter. > Some areas may have not burned, other areas only burned > the understory, some with limited burning of trees and other with full > tree killing canopy burns. The effects of these will also depend on > the specific species that burn. So to convert and entire area inside a > fire perimeter to one land cover without extensive surveying would > likely be in error.
(Please take further discussion of this thread to the tagging list https://lists.osm.org/pipermail/tagging/2020-September/055496.html ). James, this is all well known and part of the intended solution (to better map) here, thank you for pointing this out. There is no intention to "convert an entire area" inside of the fire perimeter, rather careful RE-mapping of SELECTED areas which have ACTUALLY burned (e.g. a natural=wood area is shrunk to where trees remain and "no data" or "blank map" is what remains of the burned area). This will likely best emerge when newer imagery data become available. > It seems as though the perimeter tag is the most verifiable at this point. Yes, to be clear: this fire=perimeter polygon intends to delineate the area where, as they become available, newer imagery data which display fire damage should be used to update the map. In short, the polygon conveys "here is the EXTENT of the area that burned: while it isn't yet clear whether existing landcover natural=* tags need to be altered, that is likely, as there was a major fire inside of these bounds." That's all, really. This is a 140 square mile rural area, formerly heavily/primarily wooded, not a few blocks of residential or commercial landuse, as are many typical urban fires. "Huge" is about right. At least one person (a HOT technical manager, also a firefighter) said (on the tagging thread and in off-list emails to me) that such polygons can serve a historical purpose by remaining in OSM, though I see little purpose in doing so for extended periods of time, believing that after the map is updated with newer imagery, the polygon's (initial) purpose is exhausted and can be removed from OSM. His arguments for why it should remain have to do with better building polygons enclosed by the perimeter during HOT re-mapping and into the re-population and re-building phases in landuse=residential areas that happen after a major fire. As a firefighter (and HOT mapper), he finds such data helpful, as in that case, a fire=perimeter polygon remaining is valuable history. That could last years, perhaps decades, I'm certain the effects of this fire will be long-lasting: many of the millions of trees that were destroyed were several hundred years old. Either way (the polygon is long-lasting or ephemeral to the extent it aids better landcover mapping), it is a lightweight data structure, tagged with only three tags (fire=perimeter, start_date and end_date), it remains invisible to all renderers (that I know of) and is intended to aid mappers determining "should re-mapping of landcover happen HERE, in or out?" I find that balance of data vs. usefulness "worth it." SteveA _______________________________________________ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
