In the recent decades, we have witnessed the rapidly growing popularity of location-based systems. Three types of location-based queries on road networks, single-pair shortest path query, k nearest neighbor (kNN) query, and keyword-based kNN query, are widely used in location-based systems. Inspired by R -tree, we propose a height-balanced and scalable index, namely G-tree, to efficiently support these queries. The space complexity of G-tree is Ω(VlogV) where V is the number of vertices in the road network. Unlike previous works that support these queries separately, G-tree supports all these queries within one framework. The basis for this framework is an assembly-based method to calculate the shortest-path distances between two vertices. Based on the assembly-based method, efficient search algorithms to answer kNN queries and keyword-based kNN queries are developed. Experiment results show G-tree's theoretical and practical superiority over existing methods.