A symbol map puts a mark, usually a circle, on each location and sizes it by a measure. Double-click City and Tableau places a circle on every city, because a city is a point, not an area.
Drag a measure to Size and the circles grow with it. On a state map, putting a measure on Size switches the Automatic mark from filled shapes to circles too: a shape can't change size, a circle can.
Size and color each carry one measure. Size reads best for amounts (sales, trips), color for rates and ratios (profit ratio, share). Using both on one map answers two questions at once: where the money is, and where it's earned well.
Cities need a state to be placed without doubt. Our data has one city of each name, so City alone works; in real data, add State to Detail so that, say, two cities called Portland land in the right places.