How do I lock shape positions in Visio 2010

[redwards60]

I am using MS Visio 2010...



I inserted a state map to be used as the background of the Visio drawing - I even identified it as a layer. I want to place symbols on the map, that denote certain entities, like hospitals, etc. However, every time I go to re-position the map or change the size of the map, the individual symbols lose their proper location on the map. How do I "lock" the symbols on the map, so if I move or re-size the map, they adjust accordingly so they remain in their proper location on the map?

Do I use layers, groups, containers, or something else to accomplish this?

Thanks for any help you can provide - I am self taught, so there is much in Visio I do not completely understand and use properly!