Various stuff in the import catalogue has different tags to mark up the data, you should claim some namespace and mark it as DNSC:last_updated = 2003 or whatever.

Currently mkgmap doesn't render any sort of aerialway such as the piestes on your map. However you can add it to the features file in mkgmap's resources/ directory or pester the devs to do it.

I don't know if the garmin format itself supports rendering piestes using a style designed for that purpose, but you could always hack around that and render it as highway=primary or something.

I haven't tried Merkaartor in depth but JOSM has the same feature, and in addition it has a feature that allows you to snap the building shape you've drawn so that its corners conform to 90 degrees. Which is very useful because when you draw them by hand corners that should be 90 degrees tend to be -+ 5 degrees that.

If you can find that feature in Merkaartor you can trace buildings even more accurately.

It's not on Google's map and it doesn't have a name on map24.

There's no agreed-upon tagging schema for tagging seasonal roads. You could invent something like `impassable_from=Dec-Mars` but then you'd have to get applications to support that, and some data formats OSM is exported to might not even be capable of it.

You could do what you suggest and remember to change the road at a given time each year to have `access=no` but ultimately that's in inadequate solution. You can't expect that users will download data in the time frame they expect to use it, and even if they do download it from Dec-Mars they'll have no idea from looking at the data when the road will become passable again.

There was a discussion on the osm-talk mailing list about this recently if I recall correctly. Perhaps you want to track down some other people interested in this and see if you can come up with a solution?

It's great that they're following up the Beijing Olympic map with a more general rollout. I can't wait for an OSM map of my area (Reykjavík, Iceland) on flickr.