[OSM-newbies] changing one node into a roundabout

[Lars Aronsson]

Iván Sánchez Ortega described two (or three) methods to convert a 
crossing to a roundabout.  But here's how I do it, in JOSM:

First you have a crossing at A.  Add the nodes B, C, D as follows:

            |
            C
            |
  -------B--A-----------
            |
            D
            |

Select nodes C and D, press P to split.  Select the horizontal 
(east-west) way and nodes A and B, press P to split.  Select the 
short way between A and B, press D to delete. Move the node A to 
the right.  Now you have this:

            |
            C
             \
  -------B    A--------
             /
            D
            |

Select the short way C-A-D and the node C, press N to extend.  
Click B, then click D, to complete the roundabout.  If necessary, 
press R to reverse the direction.  Add the appropriate tags.

Now, roundabouts existing of just four line segments were quite OK 
a few years ago.  Today I often add a middle node to each segment, 
then select all eight nodes and press O to make a nice circle.

It takes a little practice to get used to the craft.  To select 
multiple things, press S, click the first thing (way or node), 
then hold down shift and click on the next thing.

In the first step, adding the nodes, you need to press S (select), 
click on the empty background to make sure you have nothing 
selected, then press N (or A) to add new stuff, then click on the 
way at B. Repeat (S, click, N, click) to create C and D.  If you 
already have a node selected when you press N (or A) and click 
somewhere, you will not add a new lonely node, but a new line 
segment from the old node to the new position.  If you make this 
mistake, undo is Ctrl-Z.  Or is there an easier way to "select 
nothing" before adding nodes?


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se