OpenStreetMap
I'm trying to figure out how to map a riverbank. Ive read the wiki and it's not clear on a step by step process and doesnt work for me. I drew the river, I drew the river bank as a closed object. I tagged them accordingly, but I dont understand what "relation" is supposed to even do! If I highlight the riverbank, then click presets, relations, multipolygon, the pop up window says selection unsuitable. What the hell is a relation!? Should I be using it in this way and how do I use it. Plan non geek speak appreciated.
Discussion
Comment from c2r on 20 ஆகஸ்ட் 2010, 07:09
relations are for tagging multiple ways with the same "thing"
For example, Euroroute E15; this will encompass a number of different roads, junctions, bridges.
Or National Cycle Routes in the UK. Or Long Distance Paths....
Comment from lyx on 20 ஆகஸ்ட் 2010, 07:09
First: If your river doesn't have any islands, you probably don't need a relation; drawing the riverbank as a closed way (= area) should do fine.
A relation is used to group together "things" (ways, areas, nodes, other relations) and to describe how they relate to each other. Most common use is probably multipolygon relations, in the usual case they group together areas and describe which ones are inside one of the other. Imagine a lake with one island: You would have a multipolygon relation with two members: the area of the lake and the area of the island. To describe how the members of a relation relate to each other, they are given a "role" (one for each member); in our example the lake would have role "outer" and the island role "inner".
As Potlatch (the map editor on the website) does not work on my computer, I can not tell you how to edit a relation with it, but hopefully someone else can do so.
Comment from c2r on 20 ஆகஸ்ட் 2010, 07:10
I think they do apply to riverbanks as well, to mark them as part of the same river - but that use is a bit beyond me, sorry...
Comment from EdLoach on 20 ஆகஸ்ட் 2010, 10:14
Also, I've never got the Presets, Relations, Multipolygon menu option to do anything useful in JOSM and do the following instead:
* select all the items I want in the edit pane (shift-click on each)
* in the relations pane (may need opening first using button on left hand bar), click the button to create a new relation (use tooltip to check, think it is the left one under the list of relations)
* click the arrow button to add all of the selected elements (right pane) to the relation members list (left pane)
* in the top pane add the tags:
type=multipolygon
(and whatever the outer way(s) represent so perhaps waterway=riverbank)
* in the relation members list ensure the role for each element is set to inner or outer as appropriate (where outer represents the riverbank in your case and inner a "hole" or island).
Sorry if any of the above is too geeky.
But as lyx says - if you don't have any islands you might not need a relation, although you might if your riverbank section is made up of more than one way (then they'd all be "outer" ways).
Comment from Rogerdodger on 23 ஆகஸ்ட் 2010, 17:54
I don't even know if you guys that replied are notified when I make a reply here. I think the whole relations Multipolygon thing is a bit too advanced for me at the moment. the replies here really didnt make any sense to me. The river sections I wanted to mark do have islands.