For sure that’s an easy definition. But if it’s based on MY intention, whether MY edit is vandalism or not, how would YOU (or anyone else) know what’s my intention and that it should be not applied to the diff-files?
I might have deleted all the railways because I want to “destroy” (maybe rather call it harm) OpenRailwayMap. I might have done that by mistake or because I totally believed that’s a good thing to do.
For users of the OpenRailwayMap my intention doesn’t matter. Their map was vandalized by me. For users of the Cycle Map it’s no vandalism, since nothing is destroyed on their map.
Some maps are only limited to a certain area. For example WanderReitKarte is only available in parts of Europe. Their users don’t mind any vandalism in North America or Asia.