Since I’ve been working on updating the wikipedia page for the Port of Leith, Edinburgh, I was curious about trying to map the progression of the docks and reclaimed land over the years. There are quite a few old maps available from NLS that could be used, but I gather from reading a few posts on here that coastlines may not be straightforward in OHM.
Any pointers on this would be appreciated, as I don’t seem to be able to find any OHM specific tagging guidance for the coastline, all the links seem to go to the main OSM wiki.
Is this maybe not a good introductory task for OHM?
Unfortunately we don’t really have a good way to map coastal changes at the moment. Basically what you have to do is add “water” (natural=water) and “land” areas (various natural/surface/landuse tags which represent whatever is going on) over the top of the existing coastline – you aren’t really changing the coast but “hiding” it underneath whatever you’ve added. (Think of it like adding a river on top of land or a pier on top of water – aesthetically it has “replaced” it but it’s really just on top of it.) It’s kinda hacky but AFAIK it’s all we have right now.
OHM does have ways representing the coastline like OSM, but what is actually drawn on the website is based on a separate data source that I don’t think we can access (please correct me if I’m wrong). You can however use the existing (unused) coastline ways as parts of multipolygons.
If you’d like some examples I’ve done quite a lot around the Spey estuary and up to Lossiemouth but it’s probably quite difficult to follow since there are a lot of overlapping multipolygons representing water, wetland, woodland, scrub, beach etc for several different dates. A simpler one I’ve done is the mouth of the Vistula which only has a few iterations and is much simpler. You could also have a look at the IJsselmeer/Zuiderzee in the Netherlands. For the Port of Leith I’m not sure what you’d use for the “land” parts tag-wise.
With regard to the Port of Leith specifically I have actually mapped out some of it (based on the NLS OS maps) in the process of mapping the admin boundaries in the area, although only the bits that correspond to admin boundaries, and much of the natural coastline is quite rough. Oh, and avoid using the 1:2,500 A ed. OS map for Leith Harbour – the sheet hasn’t been properly converted by the NLS so it is very vertically distorted (use the 1:1,250 A ed. instead, it’s a higher-res map anyway).
Aside from the hacky nature of it I don’t think there’s anything particularly difficult about doing these pseudo-coastlines. (In fact the hackyness probably makes them a bit easier since really all you’re doing is “covering up”/“hiding” the existing coast rather than directly interacting with it.)
Thanks for your detailed response, and more options to look at. I’ll take a more detailed look at these in JOSM so that I can filter things better than in ID.
I’ll maybe have a go with a few of the smaller docks to start with, and see how I go from there.