[openrailwaymap] change train protection system tagging

Hi, a few minutes ago I have read a Github issue at ORM's Github repository. Because my comment proposes a (large) change in tagging, I publish it here and not at Github. https://github.com/rurseekatze/OpenRailwayMap/issues/64 The issue asks to render railway lines (the ways) in signal layer in different colours depending on the train protection systems which are installed there. As already implemented in maxspeed layer, ways without information should be rendered in grey (or another unimportant colour). Tracks without train protection should also be rendered (e.g. red). I think that we first should change tagging of train protection systems to be able to show railway tracks without train protection system (black) and without train protection system tagging (grey). With current state of tagging, we have to query dozens of tags to be sure that a track has no train protection system. Current tagging is very Germany-centric. If ORM were a map only for DB, ÖBB and SBB, this would not be a problem. If we want to be a good train protection system map, we now have to query AT LEAST following tags: * railway:pzb * railway:lzb * railway:etcs * railway:crocodile * railway:zub * … We should change tagging to three or four keys for different system categories and should give the installed systems by a semicolon-separated value list. The categories should be: * railway:train_protection:point for systems like PZB and Integra Signum * railway:train_protection:continous for systems like LZB * railway:train_protection:etcs=yes/1/2/3 for ETCS (it is so important that it should has its own key) Do you think that we need more keys? Examples: * typical German main line: railway:train_protection:point=pzb * typical German high speed line (generation 1–3): railway:train_protection:point=pzb + railway:train_protection:continous=lzb * Leipzig–Berlin: railway:train_protection:point=pzb + railway:train_protection:continous=lzb + (a tag for ETCS) * Singen–Schaffhausen: railway:train_protection:point=pzb;integra_signum Best regards Michael