How can I have e.g. all highway speed cameras displayed on the map, i.e. what is the URL syntax to search OpenStreetMap for certain tags? And where is this information (tagged locations, POIs etc.) coming from, is it collected/contributed by OSM community members or does the OSM project also use third-party sources (private/public/proprietary) and do private persons, companies, governments etc. have the power to censor/block/redact such information?