# Can't find Proj4js library

Using latitude/longitude functionality with pre-projected GeoJSON in Highcharts Maps requires the
[Proj4js](http://proj4js.org) library to be loaded.

It is recommended to utilize TopoJSON for Highcharts v10 and above, as built-in projection support is included and no third-party library is required. For more information, see the [Highcharts now prefers topojson maps](https://www.highcharts.com/blog/tutorials/highcharts-now-prefers-topojson-maps/).