latitude-longitude

Given a database of places with Latitude + Longitude locations, such as 40.8120390, -73.4889650, how would I find all locations within a given distance of a specific location? It doesn't seem very efficient to select all locations from the DB and then go through them one by one, getting the distance from the starting location to see if they are within the specified distance. Is there a good way to narrow down the initially selected locations from the DB? Once I have (or don't?) a narrowed down set of locations, do I still go through them one by one to check the distance, or is there a better

I'm writing a program which expects a number of lat/long points, and I convert them internally to UTM in order to do some calculations in metres. The range of the lat/long points themselves is quite small -- about 200m x 200m. They can be relied on almost always to be within a single UTM zone (unless you get unlucky and are across the border of a zone). However, the zone that the lat/longs are in is unrestricted. One day the program might be run for people in Australia (and oh, how many zones does even a single state lie across, and how much pain has that caused me already...), and another day

I will explain. I managed to have a draggable pin on a map. I want to retrieve the coordinates of this point and put them into two fields: Latitude and Longitude. These coordinates will later be send to a SQL table via PHP. Here is an example of what I intend to do, but instead of several pins, it's just one and it's draggable. The problem is: I'm not even able to display the coordinates of the initial point. And of course when the user moves the pin, I want the coordinates to change as well in the fields. I hope I made myself clear. What did I do wrong? Should I use the Geocoding service?

I have a database populated with roughly 10k rows currently. All of them have a longitude/latitude based on the center of a zipcode. I found a query that I am now attempting to expand on, but all in all it works well to a point. However, in my example below I am trying to find things within a 25 mile radius, which in all seems to work for the most part. Most of my results do yield within the 25 mile criteria, however I am getting a handful that are way off anything from 86 miles to 800 miles off the mark. Example: This is my center lat/lon: 37.2790669,-121.874722 = San Jose, CA Im getting