"If you have a word with the Police in any town, large or small,"

It also depends what company you keep too, anyone living in social housing or who has family and/or friends who are, or indeed anyone in contact with services like NEEDAS will probably be aware of the dodgier local areas simply because they become well known within a particular strata of the community via the grapevine. While most social housing tenants will probably want to keep out of such areas, you will get those who actually want to exchange TO them, specifically because they will be closer to their community of dealers & fellow users. So you end up with an osmosis, whereby certain locations (it could literally be a single street) will effectively develop a reputation as "drug central" for that town and even maybe further afield. I can think of a couple of such locations not too many miles from me right now.