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Building Terravision(2021) using and Carto

Eddie MG12 min read

Screenshot of demo website homepage with dummy articles and map interface displaying article location.

Adding a detailed and interactive map to a web app can be a time consuming process. Pairing and carto with react can make it pain free. Using Carto to manage your data and to render it can make for a great developer and user experience. Resulting in a web app rich with detailed and engaging visualisations.

TLDR: skip to case study section if you’re too cool for context…


At the beginning of the Netflix show The Billion Dollar code, you’re introduced to two German developers, Juri Muller and Carsten Schlute. As the series progresses we learn more about Terravision, an application that the two developers and their team (ART+COM) develop that closely resembles the modern day map software we are all familiar with, Google Earth. The series takes place in the 90s and hence the algorithms and mapping software that we use today has progressed significantly from the first versions of Terravision and Google Earth.

Nowadays, as a web developer, the inclusion of a map in your application can surpass the simple use cases provided by the google maps API. Whether it be needing to display a dynamic view of nearby taxis for your journey home or a heat map showing what people in your city are up to; maps in modern day applications are rich with information and data. Two tools that can be used to build rich map visualisations in web applications are Carto and

Simply put, Carto is a data warehouse that specialises in data for geospatial analysis with some magic under the hood.

Screenshot of Carto data catalogue

If you’re building an application that requires demographic data detailing the populations of cities in Europe just search through the catalogue, get the URL of the data set and import it using their API. Carto is built with developers in mind and hence they have a great API that pairs really well with the second tool I’ll be talking about, deck gl. If you make a call to their SQL api to obtain the data you’ll see a result containing demographic data mapped to a set of long lat coordinates. This format (GEOJSON) is an industry standard that can be interpreted by most mapping software but can be tedious and cumbersome to generate manually so it’s great to have an easily accessible source.

Note: For readers in the UK another great source of geospatial data is the ONS.

Screenshot of ONS Contour dataset

So now we have our maps and the data to enrich them. We need a way to combine them and display the result in our web app. is a software specialising in mapping and geospatial visualisation. It offers a react library designed to create high-performance web-GL based visualisations for large datasets. Hence it’s one of the easiest ways to integrate geospatial visualisations into your applications. The library is really intuitive and highly optimised out of the box. It also contains a bunch of different features that will fit a large number of use cases required by your application.

Case Study

Let’s talk through a real world example. Say you’re an international news company and you want to revamp the user experience of your website. You cover news stories all across the globe but you’ve gotten feedback from users saying finding new, interesting stories can be difficult and your team has proposed a new map interface to display all the current popular stories. As well as displaying the stories on the map you think it would be nice to supplement the articles with contextual information about the countries you’re covering (GDP, HDI, Life Expectancy, etc).

Slight caveat. Unfortunately, Carto is not a free piece of software so for the example I will be using a dataset that I’ve downloaded from Kaggle. Hopefully talking through the full process that I have to follow to integrate a generic dataset into our application and how it differs from using Carto will allow me to highlight the convenience of using Carto in your workflow.

The Data

To begin with you’ll need to source the data for the contextual information. As noted above, a quick search on Kaggle you can find a list of demographic indicators for all countries in the world. Granted this is outdated but this is where something like Carto comes in handy as it provides up to date data in the required format.

Screenshot of Kaggle data schema

Using with next.js and react

Now we have our data, the next task is to set up your project. works with react out of the box so you can use the next project starter to generate a react project and get going from there. Firstly, you’ll need to create a DeckGL component for your page. This is where all of your geospatial visualisations will sit.

<DeckGL initialViewState={INITIAL_VIEW_STATE} controller={true}>
  <StaticMap mapboxApiAccessToken={MAPBOX_KEY} />

The above code snippet would display a simple map on the page where you render the DeckGL component. You will see there’s a child component StaticMap. This child handles the map element of our page. can easily integrate with mapbox so all you need to do is create an account and use the public token to add a map to your component.

Screenshot of map on homepage

As you can see the map currently takes the whole of our page but we need to limit it to the hero section of the screen so we can see the articles as well. Adding the following prop to our component allows us to add some styling:

views={[new MapView({ width: '100%', height: '44%' })]}

The resulting page:

Screenshot of styled map on homepage

So now we have our map displayed on the homepage of our website, the next task is to take the geojson data we downloaded from Kaggle and add it to the map. For this I’ve opted to store the layers in the state which is populated when the page mounts. Using getStaticProps, I read the json file from disk and pass it as a prop to the homepage. This prop is then used to dispatch a redux action that takes the json data as an argument and returns the layers.

Note: The format of the geojson data is not fully inline with what expects (one reason why using Carto would be nice here) and hence I have to do some transformation on data load. An alternative solution here would be to process the data once yourself and then have this loaded into the app when the page mounts.

I handle the creation of the layers inside a redux saga. For the geojson data I create a new instance of the PolygonLayer class.

// Create basic polygon layer from geojson data
 const europeLayer = new PolygonLayer({
   id: 'real-poly-layer',
   data: action.payload.geoJson,
   getPolygon: d => (d as { type: string; geometry: { type: string; coordinates: Position[][] } }).geometry.coordinates,
   getFillColor: [160, 160, 180, 200],
   getLineColor: [0, 0, 0],
   getLineWidth: 1,
   lineWidthMinPixels: 1,
   pickable: true,
   stroked: true,
   filled: true,
   wireframe: true,

So we now have an instance of a polygon layer generated from the data read from the disk. The last thing to do now is add it to the component.

layers = { mapLayers };

The result:

Screenshot of styled map with polgon layer

As you can see we now have a polygon layer displayed on our map but none of the additional information included in the geojson is visible to the user. Most of’s layers can be configured to display tooltips on top of the layer. The pickable prop that I added to the PolygonLayer allows the component to access all the additional information and adding a getTooltip prop to your deck allows you to manually configure the structure of your tooltip.

getTooltip={({ object }) => {
if (object) {
    const typedObj = (object as unknown) as {
    properties: { story?: string; scalerank?: number; sovereignt?: string; level?: number; type?: string; geounit?: string; subunit?: string; name?: string; name_long?: string; economy?: string; continent?: string; pop_est?: number; gdp_md_est?: number; income_grp?: string }
    if ( {
    return `Name: ${}\nContinent: ${}\nGDP: ${}`;
    } else {
    return `City: ${}\nStory: ${}`;
} else {
    return null;

Now you can see any specific data that you want when the user hovers over a certain section of the map. Without any need to specify coordinates, boundaries etc. Everything is handled for you.

Screenshot of styled map with polgon layer with tool tips

The last feature we need to add to our map is an icon layer showing where the stories we have on our site come from. In the same saga I mentioned earlier we need to instantiate a new IconLayer class.

// Initial story data that could be pulled in from database
 const pointData = [
   { properties: { name: 'Chavignol', story: '5 Cheese Hacks Only the Pros Know' }, coordinates: [2.844560, 47.397411] },
   { properties: { name: 'Milan', story: '11 Hottest Street Light Trends for 2022' }, coordinates: [9.195585, 45.467905] },
   { properties: { name: 'Kyiv', story: '9 Best Practices for Remote Workers in the Shark Industry' }, coordinates: [30.479160, 50.44044] },
   { properties: { name: 'Zurich', story: '10 Ways Investing in Maple Syrup Can Make You a Millionaire' }, coordinates: [8.519453, 47.385598] },

 // Icon layer based on the story data above
 const layer = new IconLayer({
   id: 'icon-layer',
   data: pointData,
   pickable: true,
   iconAtlas: '',
   iconMapping: ICON_MAPPING,
   getIcon: d => 'marker',
   sizeScale: 15,
   getPosition: d => (d as { coordinates: Position2D; exits: number }).coordinates,
   getSize: d => 5,
   getColor: d => [50, 168, 82, 255],

The result is a map containing information about both the countries we’ve specified and the stories on our site.

Screenshot of styled map with polgon layer with article points overlayed

Note: In the real world we would have the icon layer pull from a database so that it’s automatically updated on publishing of a new blog.

Technical Deep Dive

You’ve now seen how easy it is to display rich maps using and Carto. I want to take some time to talk about what makes them such interesting pieces of software. In the world of geospatial analysis there are some standard data formats (GeoJSON, Shapefile, KML, CSV, etc) and ArcGis is considered to be at the forefront of the geospatial data handlers. You can think of an ArcGIS server as blob storage with an API for processing and access (although in reality it’s A LOT more complex and feature rich). The ArcGIS server is configured to interpret and process data in a geospatial format and make it easy for developers and analysts to use it where appropriate. Carto can act as both an intermediary or a replacement for ArcGIS. But using it as part of your stack can vastly optimise your load times and improve developer/user experience due to the way it handles your geospatial data.

The Power of the_geom

Let’s talk through another example, you want to create a polygon layer to display on a map of Europe to show the most recent population of each country. To generate this you would need three things:

So now you have the data, where will you store it? Well for a single country you will likely have millions of data points outlining its boundaries which can amount to ~1GB of data for each country. There are 44 countries in Europe. Now you have to load ~44GB for the user each time they want to see this visualisation. Carto offers a great solution to this. Instead of storing the contour data for a country on a point-by-point basis, it takes the data you’ve scraped from the internet (GEOJSON for example), ingests it and converts it into what they call the the_geom. This compresses millions of data points into one, which can easily be queried, manipulated or converted back into the GeoJSON format all using standard SQL commands. Now you’ve gone from having to load millions of rows of data to only 44.

So we have our data compressed and stored on the Carto servers which can easily be accessed using the Carto API, now we need to figure out how to get it displayed on our map.

More tiles than the kitchen floor

On the homepage states it’s a webgl powered framework for large scale datasets. Given how the size of geospatial datasets can quickly grow, having a library that can process and handle large volumes of data on the web is key to building an application with a good user experience. Some of the features I find most interesting are:

The End…?

So you’ve now seen how easy it is to add data rich map visualisations to your web applications. You can see all the code I used to build my demo app here and the link to the actual site TerravisionNews 2021. Any questions feel free to get in touch, PRs/comments welcome.

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