Last article I read on that said that we need a few weeks at minus 25 to get rid of the ash borer. Anything less doesn't penetrate far enough into the tree to get them all. We didn't quite get there so all we've done is slow them down.
Using my neighborhood for reference, I'd say the map shows all the ash trees.
It is my understanding the city is taking down weak or diseased ash trees (not necessarily with ash borers) and replacing them with other species at this stage. The idea is to get ahead of the ash borer by planting a greater variety of street trees. Then when more ash trees are actually infested and need removal, taking them out hopefully won't leave entire blocks with no trees at all.