You don't need to use loadClass(), you can just 'include' the class file.
Generally, you try to move everything you can into the class file so the snippet is very minimal with just the newObject() call and a few selected calls to methods of the object.
If you're storing locations in a simple custom DB table, you might check this out so you can use xPDO with them:
http://bobsguides.com/custom-db-tables.html.
If you'll have multiple tables with relationships between the tables, you'll need to look at this:
http://rtfm.modx.com/display/revolution20/Using+Custom+Database+Tables+in+your+3rd+Party+Components.
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MODX info for everyone:
http://bobsguides.com/modx.html