[Tagging] Additional detail of Levee mapping via embankments
johnw at mac.com
Wed Nov 20 05:10:10 UTC 2019
> On Nov 19, 2019, at 12:49 PM, Joseph Eisenberg <joseph.eisenberg at gmail.com> wrote:
> Is there something else that we are expecting could be done by mapping
> this in great detail which cannot be done with a simpler
> representation + a DEM?
I understand that, topographically speaking, we can get information about it from another source and see the mound of dirt. In that sense, you are correct.
But just as we show red diagonal lines through military bases, we should convey the extent of this man-made structure beyond inferring it’s existence from the road access limitations and other mapped barriers (fences, lack of roads, grass, scrub, etc). the height is just one feature of the structure that is massive and dominates the surroundings.
- just as we tag hedges and guardrails and other barriers that are not gates and bollards directly on ways, understanding there is a massive man-made barrier nearby is useful. It really limits access. A small levee can be stepped over in a few steps. These you have to climb. Both cannot be represented by a way (IMO).
- I like tagging the detail of some things. It is useful to me and others to visualize the situation. Roads there are weird and complicated - explained only by being on the levee. We have roof:part and bridge:support and =tree other details for other objects of interest, and these giant structures seem worthy of being rendered differently than just the topo contours like the the side of a hill. I will be mapping them *anyways* to set their landcover, so having a scheme to map them is “free” mapping detail.
- everything large should be represented with an area. I have 600m wide rivers. I have sluice gates you could drive a bus through. Levees wider than apartment complexes. All of them are things people see and navigate around as they traverse the levee, and correctly conveying to them “this is that levee” helps people orient themselves and properly plan their routes when moving in-on-around the levee. Right now, I can map the river, and I can map the ground cover, but not the structure - unlike other man-made structures (dams, bridges, buildings, parking lots, railway corridors, etc). Infrastructure, even giant piles of dirt, should be represented in a base map.
- levees are a function. They block water. Their construction is of an inter and outer embankment. They move separately and branch and move, so representing the levee requires (IMO) mapping the embankments and the top - all three are “features” of the levee. Mapping the two embankments in a relation gives you the “top” for free.
- Between the raised tollways that sit on 5m high raised road beds across my entire region and the hundreds of KM of levees, I have a lot of man-made piles of dirt that severely restrict access kris-crossing everything. And the levees are often adjacent *many* public amenities - parks, sports grounds, cycling roads, and other *heavily used* features.
- they are very very important during a flood. In some areas, they might be the only safe spaces. They are covered with emergency spaces and other areas safe in a flood. Understanding you are “inside” the levee Vs “outside” the levee might be the difference between life and death. If a levee breaks, the only safe space might be on top of it. Mapping and rendering these structures makes it obvious to everyone where it is without inferring it from topo information.
- they are known landmarks.
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