Introduction

Spatial queries are an essential component of location-based applications, allowing us to work with geospatial data and perform operations such as finding nearby places, searching within a specific radius, and determining the distance between two points. GeoJSON, a format for representing geographic data, provides a convenient way to model and store geospatial information. In this blog post, we will explore how to implement spatial queries using GeoJSON and JavaScript GraphQL.

Prerequisites

To follow along with this tutorial, you should have a basic understanding of JavaScript and GraphQL. Additionally, you will need a supported JavaScript environment such as Node.js, a GraphQL server, and a database that supports GeoJSON queries. For the purpose of this tutorial, we will be using MongoDB as our database.

Setting Up the GraphQL Server

First, let’s set up a GraphQL server using Node.js and the popular apollo-server-express package. Install the required dependencies by running the following command in your terminal:

npm install express apollo-server-express graphql mongoose

Next, create a new file called server.js and add the following code:

const express = require('express');
const { ApolloServer, gql } = require('apollo-server-express');
const mongoose = require('mongoose');

// Connect to MongoDB
mongoose.connect('mongodb://localhost:27017/mydatabase', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const typeDefs = gql`
  type Query {
    placesNearby(latitude: Float!, longitude: Float!, radius: Int!): [Place]
  }

  type Place {
    id: ID!
    name: String!
    location: Location!
  }

  type Location {
    type: String!
    coordinates: [Float!]!
  }
`;

const resolvers = {
  Query: {
    placesNearby: async (_, { latitude, longitude, radius }) => {
      // Implement the spatial query logic here
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

const app = express();
server.applyMiddleware({ app });

app.listen({ port: 4000 }, () =>
  console.log(`Server running at http://localhost:4000${server.graphqlPath}`)
);

In the above code, we define a basic GraphQL schema with a single query type placesNearby, which takes latitude, longitude, and radius as arguments and returns a list of places nearby. The gql function is used to define our GraphQL schema.

Implementing Spatial Queries

To implement spatial queries, we will make use of MongoDB’s geospatial indexing and query capabilities. Update the placesNearby resolver in the Query object with the following code:

placesNearby: async (_, { latitude, longitude, radius }) => {
  const places = await Place.find({
    location: {
      $near: {
        $geometry: {
          type: 'Point',
          coordinates: [longitude, latitude],
        },
        $maxDistance: radius,
      },
    },
  });
  return places;
},

In the code above, we use the $near operator to find places near a given coordinate. We specify the $geometry field as the point with the provided latitude and longitude. The $maxDistance field specifies the maximum distance in meters from the provided location. The query returns the list of places sorted by their proximity to the provided point.

Testing the Spatial Query

To test the spatial query, we can use a GraphQL client or a tool like curl. Open a new terminal window and run the following curl command:

curl -X POST \
  -H 'Content-Type: application/json' \
  -d '{ "query": "query { placesNearby(latitude: 40.7128, longitude: -74.0060, radius: 1000) { id name } }" }' \
  http://localhost:4000/graphql

In the above command, we send a POST request to the GraphQL server with a GraphQL query in the request payload. The query asks for places nearby the coordinates (40.7128, -74.0060) within a radius of 1000 meters. The server responds with the list of places and their names.

Conclusion

Implementing spatial queries with GeoJSON and JavaScript GraphQL is a powerful way to work with geospatial data in your applications. By leveraging MongoDB’s geospatial indexing and query capabilities, you can easily find nearby places and perform other spatial operations. This tutorial provided a basic example of implementing a spatial query using GeoJSON with a JavaScript GraphQL server. Feel free to explore more advanced features and datasets to enhance your location-based applications.

#techblog #javascript #geojson #mongodb #graphql