In these days, various kinds of web applications based on web 2.0 paradigm have been developed. In web 2.0 paradigm pursuing participation, sharing, and openness on the web-as-platform, web mapping or web GIS application are regarded as top most applications, so that web applications, handling geo-spatial contents, with user-interaction interface and search engine of high performance have been provided for both public users and expert users in the special domains. Public and industrial needs for web mapping mashup application by open API, linked with the practical web computing technologies, are gradually increasing. In this study, a user interface in mashup for geo-spatial feature generation was implemented by using mainly Google maps API. Spatial database resources in this implementation are those of Google mapping server. As the results, public users on web client can create their own geo-spatial data sets in web vector formats, without the help of any GIS tools or access to proprietary databases. It is concluded that web-based mashup application in client-side using open API can be used as an alternative for geo-browsing system or portable feature generation system.