maperitive: error thin river water line instead of water area

This is happening because the exported OSM data file you have doesn't contain all of the necessary objects to display the river area.

The river area (waterway=riverbank) is mapped using multipolygon relations, with the missing section in question being a relation containing five separate ways. Since at least one of those ways falls outside of the exported area, the multipolygon area is no longer complete and the area can't be properly displayed by Maperitive. The thin line that is displayed is the separate waterway=river way representing the main flow of the river.

To get around this, you could export a larger area than you need, which would hopefully pick up all of the other objects that are relevant to the ones that fall inside your area of interest. Depending on the tools you use, you may also be able to simply download the additional objects you need and add them to your existing OSM file.

A link to openstreetmap with coordinates (Like this one https://www.openstreetmap.org/#map=18/52.33018/-0.17340 ) would be useful. The screenshot looks like the river bank polygon is either unmapped or is broken. To fix this you will need to learn how to map river bank polygons. How to do this is all explained in the wiki, it isn't too hard to do, if good aerial is available, but will take some time for long sections of waterway. If you supply a link and the fault is just a broken polygon i'm sure someone will fix it.

Hi, the polygon for the river bank had the tags changed to include water=river, waterway=river, (this introduced a flow direction to the river bank). I've removed these tags and added the tag waterway=riverbank. It should be OK now.