[HOT] open geology map

Sander Deryckere sanderd17 at gmail.com
Fri Mar 13 12:59:59 UTC 2015


I think this suggestion belongs more on the general OSM talk or tagging
list than on the HOT list, but anyway.

There are already a number of ways to tag surface, like surface=*,
natural=*, landuse=*, landcover=*, ... Just read the wiki about those (f.e.
http://wiki.openstreetmap.org/wiki/Key:natural )

There's also a convention in OSM about sub-tagging. F.e. you could tag

natural=rock + rock=sandstone

Thus I guess most of what you want is already possible in OSM. You should
only try to add a few more specific conventions (f.e. about the types of
rock).

I probably don't really get your 3D attempts, but the general concensus is
that it's hard to get in certain places, and thus you can't make a uniform
map of heights or angles. As such, OSM contains no height or slope data
(apart from the elevation of some peaks), but leaves this to professionals
(such as the NASA). It isn't so hard to extract a general slope from good
precision elevation data, so there's no point in including it directly in
OSM data (with the right preprocessor, it can get rendered on the map
anyway).

So that doesn't belong in OSM, but it isn't the biggest problem IMO. The
biggest problem I see in your attempt is ignoring that OSM is a
crowdsourced effort. For crowdsourcing, you need a crowd, and that crowd is
most easily found in populated places. Your effort seems to focus on areas
with a low population (a city isn't very vulnerable for a landslide). But
sadly, there's no crowd around there, so the most we would be able to do is
some mapping from aerial pictures. This shouldn't hinder you from starting
the project, but you shouldn't have very high expectations from it.

Regards,
Sander



2015-03-12 22:03 GMT+01:00 Hazel <hlhj2 at srcf.net>:

> Dear All,
>
> Can we again discuss putting geological data into OSM? Specifically, I'd
> like a recommended way to tag fault lines and surface geology polygons.
>
> This e-mail assumes the reader knows nothing of geology, apologies to
> everyone else.
>
> First, the usecase: geological data saves lives in natural disasters, it
> is useful for common activities like agriculture, and it is interesting in
> its own right. It can also be usefully collected by amateurs.
>
> I am not suggesting that OSM should produce disaster risk maps, or
> recommendations for farmers. I am saying OSM could collect the data that
> would allow experts to quickly and easily make these things.
>
> Using OSM contours, they can work out areas of flood risk and tsunami
> escape routes. Using contours and and basic geological information, they
> can work out areas of landslide risk (landslides kill more people than
> volcanoes or floods or earthquakes, but they kill a few dozen at a time).
> If we map faults, they'll know more about where earthquakes are likely to
> happen (you know the photos of roads after earthquakes, offset by a few
> centimeters? The fault is the plane where the offset happens, and
> earthquakes use the same faults over and over again). If you map areas of
> shallow bedrock vs. unconsolidated sediment, you know which areas may
> suffer soil liquifaction in an earthquake.
>
> https://en.wikipedia.org/wiki/Soil_liquefaction soil liquifaction
>
> Technical infodump:
>
> To make a geological map, you map areas with similar surface rock or
> sediment2. You describe them (anything from field IDs like "greenish rock
> #2" to detailed technical descriptions) and give them proper names (e.g.
> "the Tunbridge Wells Sand Formation").
>
> Having mapped the boundaries between different rock types, you can also
> trace faults and the line of folds in the rocks. These all obviously exist
> in 3-D, but are usually represented on 2-D maps. Just mapping the 2-D trace
> is enough for many purposes.
>
> OPTIONAL EXTRA 3-D info:
> If you want to add more information about the third dimension to a two-D
> map, there are conventions for that. You specify a line (along the axis of
> the fold, or on the steepest line down the fault plane or boundary plane).
> You map the direction of this line. Then you measure the angle between the
> line and the horizontal, and write in on the map (next to standard symbols:
> for a plane, a T-shape, and for a fold axis, an X with two or three of the
> lines turned into arrows pointing in the two or three downhill directions).
>
> Plane:
> http://web.arc.losrios.edu/~borougt/StrikeAndDip.jpg
>
> Fold:
> http://bc.outcrop.org/images/structural/press4e/figure-11-16b.jpg
>
> Planes on either side of a fold:
> http://courses.missouristate.edu/EMantei/creative/GeoStruct/strkdip.jpg
>
> This is actually fairly easy to explain in 3-D, but not in 2-D, and I
> don't know of a good video. We could make one.
> END OPTIONAL EXTRA
>
>
> Example:
> Let's look at the Weald area of the UK, since it is well-mapped.
>
> Read:
> https://en.wikipedia.org/wiki/Weald#Geology
>
> Terms:
> "Lower Cretaceous" and "Upper Jurassic" describe age (lower means older)
> "rocks", "chalk" and "sandstone" describe rock type
> "sands" and "clays" describe sediment type
> "Purbeck Beds", "Ashdown Sand Formation" and so on are proper names of
> groups of rocks/sediments. These names are hierachical, like taxons, and
> are in databases (for the Chalk Group that forms the White Cliffs of Dover:
> http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=CK).
>
> The cross-section may help make the 2-d map make sense.
>
> To see how faults and folds (synclines/synforms, that sag, and
> anticlines/antiforms, that hog) are mapped as lines, see this map:
> https://commons.wikimedia.org/wiki/File:Geologic_map_SE_
> England_%26_Channel_EN.svg
> (just gives rock ages, not type).
>
> Faults are usually much more obvious on small-scale maps than they are on
> this map.
>
> For sediments, there exist multiple soil classifications, with mappings
> between them, and OSM could support them all, but the classes we have
> (sand, gravel...) would be enough to start with.
> Examples:
> https://en.wikipedia.org/wiki/Australian_Soil_Classification
> https://en.wikipedia.org/wiki/USDA_soil_taxonomy
> etc.
>
> QGIS is increasingly used for geological mapping, so it works increasingly
> well with many other geological tools. QGIS is already well-integrated with
> OSM. The barrier for geologists new to OSM to upload their maps is
> therefore low. Classes of students could do it.
> http://wiki.openstreetmap.org/wiki/QGIS
>
> End infodump, requests for clarification and corrections welcome.
>
> Could anyone suggest a set of minimal changes that would make it possible
> to enter data like this? As I said, just having a recommended way to enter
> a surface geology polygon, a geological contact line (between two
> polygons), and a fault line (with optional dip direction and inclination)
> would be very useful.
>
> Pseudo-3-D perfection would also allow keeners to input the contact
> between two rock formations (line, with dip direction and inclination) and
> input folds (line, with dip inclination), but this can also wait.
>
> Regards,
> Hazel
>
>
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