This book introduces Document As System (DAS), a new GeoComputation pattern, which is also a new GIS application pattern. It uses the GeoComputation language (G language) to describe and execute complex spatial analysis model in the MS Word environment, which solves the bottleneck problem of GIS application, makes GIS become a popular tool for spatial data analysis from the spatial data visualization tool, and plays an important role in the wide application of GIS technology. This book systematically introduces the theory related to the new GeoComputation pattern and the application example in the "dual-evaluation" of territorial and spatial planning, which can be used as a learning and reference manual for GIS related professionals and business personnel engaged in the "dual-evaluation" of territorial and spatial planning.