Software product line engineering aims to reduce development time, effort, cost, and complexity by taking advantage of the commonality within a portfolio of similar products. This may benefit the development of applications in several domains, and particularly in geographic information systems (GIS). Reusing services for GIS challenges developers to produce assets highly adaptable to various service clients and contexts. For that, service variability must carefully be modeled by considering different recommendations such as well-established standards. This paper presents an approach that facilitates variability implementation, management and tracing by integrating product-line and GIS development. Features are separated following standard recommendations and composed on a platform-oriented framework. The presented concepts are illustrated with a case study of a marine ecological system.