# Multipolygoner

Man ska ju använda multipolygon när man t.ex. märker ut en sjö som ligger i ett skogsområde vad jag har förstått. Jag har lyckats med det en gång, och kommer inte ens ihåg riktigt hur jag gjorde. Instreuktionerna är dåliga. Eftersom det är så krångligt, så drar jag mig för att sätta sig ner och försöka.
Kan man inte bara lägga sjön på skogen, utan att ta bort skogen under?

Synpunkter?

Sorry for english answer, but my swedish reading is very poor and writeing impossible. So i hope, i get your question. You ask, why it is nessecary to use multipolygons. For this my answer is: wich of the polygons (e.g. landuse) should be presented? Of cause it is possible to have some rules like “a house is visible”. But now take the example lake/forest. A big lake with an ilsand covered with forest → in the overlapping area the forest should be shown. Now the oppsosite. A big forest with a small lake in the middle → in the overlapping area the lake should be shown. As “layer” is used for something else here the idea of multipolygons help solving.

I also understand, that you ask how to enter these data. For this i only can help you in JOSM, but its quite easy. As the whole is only for closed ways, all my example assume we are talking about this.

1. mark all ways, which should be in the multipolygon relation (mouse click with holding ctrl key)
2. select preset / relations / multipolygons → new window opens
3. optional: enter a name
4. click “new relation” → windows closes, a new window opens
5. enter the roles for the selected elements
outer → surrounding of all (in very most cases only one element)
inner → holes in the outer (often many elements)
6. close with OK
that’s it

Just a hint: the inner landuses must be different from the outer. Example: if you have a hole in the forest give the outer landuse=forest and the inner no tag. Both inner and outer with landuse=forest is wrong.

hth

-trekki