OpenGeofiction
at “view”-mode you have a little skala left down on the screen. In “edit”-mode there is really nothing. Not helpful.
So I have seen, on my screen at zoom 16 (200m) that this 200 m are 34 millimeters on screen. How long this 200 m are on your screen, may differ logically. So I made a little strip of paper and a mark at 17 mm for 100 m, at 34 mm for 200 m and so on. That is for zoom 16. For zooms 17 (100 m) and 18 (50 m) you can set the meters too at your markers.
O.k. - is not perfect, but better as nothing. And by the time you get a feeling for the meters at the scale, in which you work. In doubt you set your paper-ruler softly at the screen
Some mesures = Great churches normally not longer then 80 m, a soccer-field 100 * 67m , one Block in Manhattan / New York 60 * 240 m, one block in the “Eixample” of Barcelona 148 * 148 m.
Discussion
Comment from thilo on 26 March 2014 at 21:37
Beware! Since Opengeofiction uses Mercator projection, the screen size of objects not only depends on the level but also on their geographic latitude.
The blocksize in Barcelona, for eixample, is only 133,3 m.
A better solution would be to use JOSM, which provides some methods to measure distances.
Comment from histor on 26 March 2014 at 22:32
You are right - 3 Blocks in the “Eixampla” are 400 m.
Logical the meters are in connection with greographical latitude. But is it not for exactly measurement, but for the dimensiones.