Web-based geographic applications are continuously evolving and are becoming increasingly widespread. Actually, many Web-based geographic applications have been developed in various domains, such as tourism, education, surveillance and military. However, designing these applications is still a cumbersome task because it requires multiple and high-level technical skills related not only to recent Web technologies but also to technologies dedicated to geographic information systems (GIS). For instance, it requires several components (e.g. maps, multimedia contents, indexing services, databases) that have to be assembled together. Hence, developers have to deal with different technologies and application behaviour models. In order to take the designers out of this complexity and thus facilitate the design/evaluation of Web-based geographic applications, we propose a framework that focuses on both designers’ creativity and model executability. This framework has been implemented in a prototype named WINDMash, a Web mashup environment that designers can use both to create and to assess interactive Web-based applications that handle geographical information.