GEOG 585
Open Web Mapping



Note: Currently, this lesson teaches the Leaflet API. If you are looking for the previous materials on OpenLayers, see the Lesson 7 archive page.

Last week, you used a server-drawn image from a WMS to display your business layer (the farmers markets). This week, you'll learn about an alternative way to display your business layers on the map; namely, sending the raw data to the client (such as a web browser) to be drawn. This is a common technique in many web maps that can provide for much interactivity and potentially faster performance if used appropriately. You may have even been exposed to this practice when you reviewed a web map for your assignment last week.

This lesson describes two common formats used for sending vector GIS data to the browser (KML and GeoJSON) and shows how you can add these types of layers in Leaflet.


  • Describe benefits and challenges of drawing thematic vector map layers on the client.
  • Choose between KML, GeoJSON, and other formats for drawing vector data on the client.
  • Understand how vector layers can be symbolized on the fly to provide a more interactive web map experience.
  • Draw thematic vector layers in a web map using Leaflet and change the symbolization in response to map events.


  • Read the Lesson 7 materials on this page.
  • Complete the walkthrough.
  • Complete the Lesson 7 assignment.