On the meaning of "downtown" and "uptown"

As far as I know, every American city has a downtown, but not every city has an uptown. The meaning of "uptown" varies from city to city, and in some cities, the term is not used at all.

Downtown always means what Brits would call the city center, the area with the highest concentration of commercial buildings, usually also the location of the tallest buildings and the most expensive land and rental space, per square foot. Historically, it is usually the approximate place where the first buildings were built, and as the city grew, it spread outwards from there. In cities that have numbered streets (1st Street, 2nd Street, etc.) the numbering begins downtown, usually next to a river or shore, and the numbers get larger the further you are from downtown. So do house numbers.

In New York, as I understand (I am not a New Yorker, so someone correct me if I'm wrong), "uptown" and "downtown" are not so much places as directions. To go downtown means to go toward the southern tip of Manhattan; to go uptown means to go the opposite direction, that is, northward. This works, and is meaningful to New Yorkers, because Manhattan is a long narrow island running roughly north-south. Development began at the southern tip and spread northwards.

Most cities aren't configured this way. Most cities began at a central location and expanded in 4 directions (sometimes only 3 directions if the city is bounded on one side by a large body of water). Either way, "downtown" has a clear meaning, while "uptown" is not likely to be used because it would be too vague. Instead, we tend to use clearer terms like "the North Side," "the East Side," etc. The exact terminology varies from city to city and depends on local history and geography.

Neither St. Louis, where I grew up, nor St. Paul, where I live now, has an "uptown." In Minneapolis, however, Uptown is the name of a secondary commercial district about 3 miles south of downtown. I don't know how it got that name. It has a high concentration of movie theaters, restaurants and bars, and trendy shops.