I have this script that will show custom markers on a google map, but I would like to include a input text-box and be able to enter a city/state and a zip-code and see if there are any markers within lets say 400 miles from that city/state or zip-code. I would love it if the map can be dynamic so as you type out the city/state or zip-code it will show the results on the map by getting rid of all the other markers and leaving only the one that is within that radius, if that is too hard then a simple alter box saying what unit is the closest will also be OK :) I searched and found some say that I should load the geometry library and use computeDistanceBetween() to find the distance of each marker from your center point but I have no idea how to do the zip-code part or how to put all of this together to work.

Here is my code: