Data granularity and transmission order are two basic questions when transferring steaming maps progressively over web. The map data with high granularity is able to result in high resolution animation but the data volume increases greatly. The transmission order reflects the data stream sequence from coarse to refined at different domains. This study investigates the hierarchical structure of map data organization and presents a granularity classification with three levels

namely feature level

object level and geometric detail level. Through example analysis

the study discusses the application of three granularity partitioning in progressive transmission as well as the strategies to reduce data volume. For transfer order analysis

a mat of semantic and scale is built to describe the map data set and two kinds of transmission order is offered to apply in different progressive transfer processes

namely the semantic priority order and the scale priority order.