地理信息系统和数据结构.docVIP

Lesson 2 GIS software and data structures The power of a GIS comes from its ability to store relationships among and between objects. There are lots of GIS analysis functions. Functions should be defined independently of technical issues, understandable by users with little technical knowledge of GIS, independently of data model. Functions are used to translate needs into specific GIS operations. List of available functions is outgrowth of past GIS user needs. Some GIS claim as many as 1,000 commands. Some of these functions are: Measure Coordinate transformation Generate objects Select a subset of objects Modify attributes of objects Dissolve and merge area objects Compute statistics for a set of objects Topological overlay Operation on surfaces Network analysis Input and output management. These functions are fulfilled by kinds of GIS software. The term best is extremely subjective where GIS is concerned. Some systems have extremely loyal followings that advocate their system over others. A best system implies that one solution is best for all problems, which is of course largely meaningless. The following subset of GIS system, most available commercially, is intended to illustrate the breadth and depth of systems on the market today and some of the major and minor differences between these systems. No endorsement is intended, and the list is provided to further the GIS “consumer ‘s “ education. Research has shown that these “big eight” packages account for the majority of those used in educational, and many professional, settings. In some cases, different GIS software packages are used in combination or along with other software for statistical analysis, graphical editing, or database management. Arc/Info Arc/Info is a long-lived full functions GIS package that has been ported to the microcomputer, the workstation, and the mainframe. Arc/Info is used to automate, manipulate, analyze, and display geographic data and incorporates hundreds of sophisticated tools