An overlay generator recognizes specific types of content and metadata present on a web site, and retrieves additional content related to the web site from other sources. The overlay generator makes the additional content available in a web browser as an overlay or as a hyperlink, so that the additional content can be viewed in combination with the original web site content. For example, if a zip code is present on a web site, and the web site includes a static map showing points of specialized interest in that zip code, then the overlay generator recognizes the zip code as a specific type of content related to maps, and retrieves an interactive map of the zip code from a map service, and generates an overlay for superimposing the interactive map on the static map, so that the content of both maps is displayed in a single integrated map.