Originally published here: https://atakua.org/w/landcover-conflation-unsolved-issues.html
This post continues where the previous one left off.
After some time spent on processing and importing land cover data, I have several ideas on how to further improve and streamline both the import process and in general work with land cover features in JOSM.
Suggested tools to help with land cover data
Certain typical tasks arise over and over again when one works with polygons meant to represent land cover, regardless of whether they are imported or manually traced. At the moment there are no adequate tools in JOSM to assist with such tasks.
The trick here is not trying to find an exact geometric solution to the tasks at hand, but rather imitate what a human would reasonably do to finish such a task. And a human would cut corners, allow some inexactness traded in for speed of completion.
Floodfill tool
A common task is to fill a gap between two or several polygons. An example would be to map a new farm field situated between several forests or clammed between several intersecting road segments. Currently one has to carefully trace a new way along the existing borders, either reusing nodes or leaving a small gap between the new ways and adjacent ones.
The idea here is similar to pouring a bucket of paint into the middle of the empty area and then letting it spread out naturally to fill the empty area. The paint will then spread out until it hits borders, or until it runs out of paint.
The same approach can be implemented in a tool that starts from a single node (or rather, from a tiny closed way) which then grows in all directions. Its growth is stopped when a segment of the new way hits a boundary in a form of an existing way. Optionally, the new way can then snap to existing way there.


Before and After map of Transjakarta Corridor 9 route, between Pluit and Penjaringan bus stops