# Leaflet [Leaflet](https://leafletjs.com/) is an open-source JavaScript library for displaying interactive maps on the web or mobile. A simple and lightweight library that will enable you to display and visualise location data and build dynamic applications. ## What you'll need * OS NGD API – Tiles added to an API project in the OS Data Hub with an API Key. See [Getting started with an API project](/os-apis/core-concepts/getting-started-with-an-api-project.md) for more information. * A text editor like Visual Studio Code or Notepad to edit and save your HTML and JavaScript files. {% stepper %} {% step %} ### Set up your HTML file * Create a new HTML file with a text editor (for example, Notepad, Visual Studio Code). * Add the basic HTML structure to your file with a placeholder `
` for the map. ```html OS NGD API – Tiles | Template (EPSG:3857) | Leaflet
``` {% endstep %} {% step %} ### Insert your API Key * To enable access to OS APIs an API Key is required. Inside the `