When spatial data is digitized for use in geographic information systems and other software, information about its original scale, resolution and accuracy is frequently lost. As a result, using such information at different scales and combining it with data from other sources may be difficult. Mapping vector data at smaller than the original scale requires its generalization, which is usually handled by post-processing in ways that are only weakly supported by databases. The models and methods described in this book overcome many such problems by providing a multi-resolution data representation that allows retrieval of map data at a hierarchy of scales, as well as documenting the accuracy of every spatial coordinate.