Stuck between two countries (US/MX)

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Also known as Hell on earth. There's a movie, starring Tom Hanks, where he plays a man who lives in the airport terminal because he has no documented country of citizenship. This is like that only far less cute. If one enters Tijuana via ground transport (or tours downtown) chances are very, very, very high that one will encounter the literal wasteland that is home to the unfortunate lot, both, stuck from making a living in Mexico and entering America.

At any time of the day individuals stand and call up to passers-by begging and pleading for alms to be thrown their way

These people, homeless, forsaken, dirty, rejected, live under the bridges in Tijuana's river. Like trolls. I suppose water once flowed through it (or maybe it still does during specific times of the year) but I've only ever seen a steady stream of waste churn through. In fact, the walls on either sides are decorated with large murals so I guess artists wouldn't do that if they expected the work to be covered by shit water. And that's about as pretty as it gets. The other, living images are a painful eye-sore.

tale of two cities 

or Upstairs, Downstairs

Typically the lost souls are illegals deported back to Mexico -- but with no connections to the land whatsoever besides nationality. That means no family, friends, jobs, resources. Some of them have grown up in America without, unfortunately, ever becoming American. Go figure. Criminals, junkies, vagabonds wouldn't be an unwarranted generalization. However some do have skills/trades; they're simply without any wherewithal to apply them. At any time of the day individuals stand and call up to passers-by begging and pleading for alms to be thrown their way.

I guess artists wouldn't do that if they expected the work to be covered by shit water

These rejects - because it's a fact: Mexico doesn't want them either - establish tent cities along the river. At night they start camp fires which stink up the air. 

In Playas de Tijuana, the westernmost section of the city along the coast and one of the preferred areas for expats, some homeless people (and regular beach goers too) start stinky campfires on the beach. A neighbor told me the homeless used to sleep under the boardwalk until authorities ran them out. Now, the homeless break off parts of the boardwalk, and whatever else is flammable, for their heat! At this rate, in a year the boardwalk will be as snaggletooth as Broom-Hilda.