I never pay attention to the blue circles ...
I prefer to think by myself : I choose the location where you have mass production, mass food, and possibly gold.
For food : the best are flood plains (food, river => irrigation => farms, gold, and after, water mills)
For production : hills/plains for mines. (or hills/green land)
For gold : gold (yes ^^), gems, silver ... (but these are more rare than specific tiles) => Or cottages on green lands, when you have enough food and production (workshops), build cottages everywhere.
You have to calculate if you'll have enough food for all : each citizen needs 2 food, so if you have some tiles that gives 1 or 0 food, you'll have to find another tile that give the lacking food.
For example, if you have a land where you have 3 hills/plains and 2 flood plains and 1 corn on green land :
=> You'll need 2+2+2 => 6 food for the 3 hills plains.
the 2 flood plains gives you 3 and 3, so you have 1 surplus for each one, so 1+1 = 2, you need 6-2 = 4 food now.
You have the corn, it gives 1 more food, so you have 3, so 1 surplus, so 4-1 = 3 needed.
You'll build a farm on it, the corn give +2 food, so 3-2 = 1 left.
If you have irrigation, it's ok, +1 => So you have all your food for your hills/plains.
If no, build a farm on a flood plain, +1, so it's also ok.
Best city lands are the ones where you have enough food to support all production tiles which do not produce food.
So at the end, you'll have all tiles occupied by a citizen, and a surplus of 2, then you can have a specialist, or you can have other "foodless" tiles to reduce the 2 to 0 to stop the growth.
If you have too much food, hope you have hills/plains, or make mass specialist but these ones are not very good compared to citizens who work on tiles with an installation.