Ever wanted to add advanced features like geo-search to your website or app, but the process felt too overwhelming?

Well, I will let you in on a trade secret! 🤫

It can be done with JUST 9 LINES OF CODE using Firestore! 🤯

Let's get started!

Add Geo-hash to your data

Before you can use geo-search, you would need to add one additional field to your data called geohash.

To generate the geohash, you can use a library called geofire-common.

npm install geofire-common

The geohashForLocation function accepts the latitude and longitude as input and returns a geohash for the location.

await setDoc(doc(db, "cities", "LA"), {
  name: "Los Angeles",
  lat: 34.0,
  long: -118.2,

  // store geohash
  geohash: geofire.geohashForLocation([lat, lng]),
});

NOTE: The geofire library is available for Swift, Kotlin, and Java too, thus enabling you to use it in your mobile apps as well.

Querying locations within a radius

After adding the geohash to your data, you can now start querying locations from the database.

const getCitiesWithinRadius = async (
  radiusInM: number,
  center: [number, number]
) => {
  const bounds = geofire.geohashQueryBounds(
    center,
    radiusInM
  );

  const promises = [];
  for (const bound of bounds) {
    const q = query(
      collection(db, "cities"),
      orderBy("geoHash"),
      startAt(bound[0]),
      endAt(bound[1])
    );
    promises.push(getDocs(q));
  }

  const snapShots = await Promise.all(promises);
  const cities = snapShots
    .flatMap((snapShot) => snapShot.docs)
    .map((doc) => doc.data());
  return cities;
};

The getCitiesWithinRadius will accept the radius in meters and the coordinates (latitude & longitude) as input & return all the cities within the specified radius.

NOTE: To keep the code clean & easy to read, the 9 lines have been broken into several more lines, if clean code isn't your thing, you can even use a one-liner.

Limitations

As Firebase docs put it:

Edge Cases - this query method relies on estimating the distance between lines of longitude/latitude. The accuracy of this estimate decreases as points get closer to the North or South Pole which means Geohash queries have more false positives at extreme latitudes.

To remove the false positives, you can use the distanceBetween function from the geofire-common library to filter out the cities that are outside the radius, which would require additional computation.

const filteredCities = cities.filter((city) => {
  const distanceInM = geofire.distanceBetween(
    [city.lat, city.long],
    center
  );
  return distanceInM <= radiusInM;
});

return filteredCities;

Wrapping up

Congratulations!

Now location-based search is no longer rocket science, but just a few lines of code away! 🚀

The world is your playground! 🎉

PS: A huge shout-out to my friend Bikram for digging into the Firebase docs & sniffing out this incredible feature

Thanks for reading

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FAQ

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1. I am a beginner, how should I learn Front-End Web Dev?
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2. Would you mentor me?
   
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