Many cities have areas that are best avoided (or best avoided after dark). Often these less desirable areas also happen to offer cheaper hotels and so people looking for an affordable hotel might accidentally be lead to these areas.
I find it hard to quickly identify these areas and in particular the areas relevant for my visits. Googling will often lead to a list of names of areas which are best avoided (provided for example by someone on reddit). However, since I don't know these cities it would take a lot of time to figure out where all these areas actually are and whether they are relevant for my stay. For example the list might contain the names of a lot of areas that could much more quickly be identified as "out of the center"/"you will probably never go there anyway" while others might be very close to downtown and important to know about but they get drowned out in the presented format. I have tried looking for crime maps e.g. https://crimegrade.org/safest-places-in-washington-dc-metro/ but this seems to be quite useless. It shows the tourist area to be the most dangerous part of the city. I don't think this has anything to do with this really being an area that should be avoided and just to do with the fact that it is normalized per resident and these areas will obviously have many more people visiting them per resident than other areas.
Is there any way to visually (without knowing the names of areas) learn what areas to avoid?
I have this question in general not just for Washington DC. For example I have to find out the same for Sao Paulo. I think it would be useful if an answer includes a general strategy perhaps with Washington DC as an example case of how the strategy works out.