sending large structures to the browser

I'm trying to create a registration page that will allow the user to create a profile and show where they live using a dynamic dependant select form. The form allows 1. continent selection 2. country selection 3. region selection. I have these working, and so far, the page seems to be loading quite quickly, even without caching the query (120 ms). But, I also want the user to be able to select their city. I will be loading three fields from a database (city name, country_id, and region_id). This dataset becomes quite large considering all notable cities in the world, and passing it to the browser causes great bog down (about 30 seconds). What do actual programmers do for sending large datasets to the browser (I'm not a programmer) btw, I am using q-forms by pengoworks to create the javascript structures/dynamic select menus (if that helps). Thanks for any suggestions!
dan