title: Best way to list all locations in a database ONLY if they are 1km away from the current location?
body: <p>The design of my app is that users place a flag on a map and this flag gets its own location and is entered into a database. </p>
  
  <p>When a user opens the app, I want to load a list of all the flags that are ONLY 1km away from them. </p>
  
  <p>I can load all the flags and do an <code>if</code> statement to check if the location is 1km away within this for loop, and just append it to the list of flags that will be listed. </p>
  
  <p>How am I able to only list flags that are 1km away without hurting the performance and loading the data of a flag that won't even be added? I'm using Firestore. I don't think this type of querying is possible.</p>