---
title: "Visualize population density | JavaScript maps SDK"
description: "Calculate and display population density using variable expressions."
---
# Visualize population density
Use a [variable binding expression](https://docs.maptiler.com/gl-style-specification/expressions/#variable-binding) to calculate and display population density.
In this example, we use the population and area variables to create a choropleth map that visually represents the population density.
### NPM module setup
```bash
npm install --save @maptiler/sdk
```
#### main.js
```js
import { Map, MapStyle, config } from '@maptiler/sdk';
import '@maptiler/sdk/dist/maptiler-sdk.css';
config.apiKey = 'YOUR_MAPTILER_API_KEY_HERE';
const map = new Map({
container: 'map', // container id
style: MapStyle.STREETS, // stylesheet location
center: [30.0222, -1.9596], // starting position [lng, lat]
zoom: 7 // starting zoom
});
map.on('load', function () {
map.addSource('rwanda-provinces', {
'type': 'geojson',
'data':
'https://docs.maptiler.com/sdk-js/assets/rwanda-provinces.geojson'
});
map.addLayer({
'id': 'rwanda-provinces',
'type': 'fill',
'source': 'rwanda-provinces',
'layout': {},
'paint': {
'fill-color': [
'let',
'density',
['/', ['get', 'population'], ['get', 'sq-km']],
[
'interpolate',
['linear'],
['zoom'],
8,
[
'interpolate',
['linear'],
['var', 'density'],
274,
['to-color', '#edf8e9'],
1551,
['to-color', '#006d2c']
],
10,
[
'interpolate',
['linear'],
['var', 'density'],
274,
['to-color', '#eff3ff'],
1551,
['to-color', '#08519c']
]
]
],
'fill-opacity': 0.7
}
});
});
```
#### index.html
```html
Visualize population density | NPM example
```
#### style.css
```css
body {margin: 0; padding: 0;}
#map {position: absolute; top: 0; bottom: 0; width: 100%;}
```
### Basic JavaScript setup
```html
Visualize population density
```
## Related examples
### [Choropleth GeoJSON](https://docs.maptiler.com/sdk-js/examples/choropleth-geojson/)
Tutorials
Create a styled choropleth map using a GeoJSON overlay.
### [Polygon layer (polygon helper)](https://docs.maptiler.com/sdk-js/examples/helper-polygon-minimal/)
Examples
Add minimal polygon layer using MapTiler polygon helper.
### [Interactive choropleth map](https://docs.maptiler.com/sdk-js/examples/interactive-choropleth/)
Examples
Use events and feature states to create a interactive choropleth map.
### [GeoJSON polygon layer](https://docs.maptiler.com/sdk-js/examples/geojson-polygon/)
Tutorials
Add GeoJSON polygon overlay to your web map application.