This study aims to identify key usability factors in a GIS (Geographical Information System) web service for mobile phone. The study also includes a usability evaluation of such a prototype. The prototype was created with the objective of evaluating the cleanliness in the city of Gävle and involving the users in keeping the city clean. Research on the subject of usability was performed in preparation for the development of the prototype. The subsequent usability test that was performed showed that the prototype was highly usable in consideration to efficiency, learnability and satisfaction. However in regards to effectiveness, the prototype was in its current state not highly usable.