The SF Chron (check the earlier links) distinguishes between "chronic homeless" and "hardcore homeless". Chronic homelessness appears to be more of an economic condition related to poverty. "Hardcore homelessness" is more severe condition, a permanent and very harsh life on the street, often related to addiction and mental illness. You might not even notice the chronic homeless in your day to day life.
Apparently, San Francisco does stand out in the high incidence of hardcore homelessness. Supposedly SF and NY have the same number of "hardcore homeless", even though SF has about 1/10 the population (though any time you get into these ratios, you have to remember that SF is a small geographic region and population within much larger bay area - if you drew a 48 square mile border around an urban core in NY or LA, the numbers probably wouldn't look so dramatically different - my guess is that SF would still look bad, but not by anywhere near this order of magnitude).
Apparently, San Francisco does stand out in the high incidence of hardcore homelessness. Supposedly SF and NY have the same number of "hardcore homeless", even though SF has about 1/10 the population (though any time you get into these ratios, you have to remember that SF is a small geographic region and population within much larger bay area - if you drew a 48 square mile border around an urban core in NY or LA, the numbers probably wouldn't look so dramatically different - my guess is that SF would still look bad, but not by anywhere near this order of magnitude).