Although the populations of the cities drive the comparative raw numbers of houses on the market, the trend lines give an indication of the strength or weakness of the markets and, generally, of what has been happening with prices. Obviously, higher inventories create more competition to sell and, therefore, greater pressure on pricing. You are likely to find the greatest bargains where inventories are highest as a percentage of total local housing stock.
Of course, like most sweeping generalizations, this one has exceptions, so take the chart and most other out-of-context data with a lump of salt. You will find the interactive map by clicking here.