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1、Chapter 1IntroductionAs in any other technical area,there can be a fair amount of technicalvocabulary to learn before a student can be comfortable with the subject.Since thistext is introductory by design,we will try to be consistent in our use of language.Much of the vocabulary of geographic inform
2、ation systems overlaps that of computerscience and mathematics in general,and computer graphics applications in particular.We provide a glossary of technical terms at the end of this text,as a reference for thestudent.1.1 GeographyGeography has been facetiously defined as that discipline which,whens
3、ome use is found for it,is called something else.Slightly more serious scholars havedefined geography as what geographers do.The German philosopher ImmanualKant set geography in the context of the sciences by stating that knowledge could besubdivided into three general areas:1.those disciplines that
4、 study particular objects or sets of objects and phenomena(such as biology,botany,forestry,and geology);2.those disciplines that look at things through time(in particular,history);and3.those disciplines that look at features within their spatial context(specifically,geographic disciplines).In a more
5、 classical sense,the word geography may be defined in terms of itsconstituent parts:geo and graphy.Geo refers to the Earth,and graphy indicates aprocess of writing;thus geography(in this literal interpretation)means writing aboutthe Earth.Another definition of geography focuses on mans relationship
6、with the land.In their writings,geographers deal with spatial relationships.A key tool in studyingthese spatial relationships is the map.Maps present a graphic portrait of spatialrelationships and phenomena over the Earth,whether a small segment of it or theentire globe.It is interesting that in a s
7、urvey conducted to determine what factorsinfluenced people to adopt the profession of geography,an early interest in maps ratedat the top of the list.There are many skills that people possess to a greater or lesserdegree.If a person speaks well,he or she possesses fluency.If a person understandswrit
8、ing well,he or she possesses literacy.If a person understands numbers andquantitative concepts well,he or she possesses(at least in Great Britain)numeracy.Similarly,there is a special skill in the analysis of spatial patterns in two and threedimensions.This skill can be referred to as graphary.Altho
9、ugh many individuals takethis skill for granted,we all know those who have difficulty reading maps orinterpreting aerial photographs.What these two activities have in common is the useof an essentially two dimensional view of geographic space,a view that helps theadept map-reader or photointerpreter
10、 to understand spatial relationships.1.2 Information SystemsThe function of an information system is to improve ones ability to makedecisions.An information system is that chain of operations that takes us fromplanning the observation and collection of data,to storage and analysis of the data,tothe
11、use of the derived information in some decision-making process(Calkins andTomlinson,1977).This brings us to an important concept:a map is a kind ofinformation system.A map is a collection of stored,analyzed data,and informationderived from this collection is used in making decisions.To be useful,a m
12、ap must beable to convey information in a clear,unambiguous fashion,to its intended users.A geographic information system(GIS)is an information system that isdesigned to work with data referenced by spatial or geographic coordinates.In otherwords,a GIS is both a database system with specific capabil
13、ities forPlanningUserneedsUseractionOutputproductsDatacollectionDatastorage麟 ManipulationA&analysisFigure 1.1 Simplified information system overview.spatially-referenced data,as well a set of operations for working with the data(seeFigure 1.1).In a sense,a GIS may be thought of as a higher-order map
14、.As we shall see later,a modern GIS also stores and manipulates non-spatialdata.Just as we have maps designed for specific tasks and users(road maps,weathermaps,vegetation maps,and so forth),we can have GISs designed for specific users.The better we are able to understand the range of needs of a use
15、r,the better we will beable to provide the correct data and tools to that user.A geographic information system can,of course,be either manual(sometimes called analog)or automated(that is,based on a digital computer).Manual geographic information systems usually comprise several data elementsincludin
16、g maps,sheets of transparent materials used as overlays,aerial and groundphotographs,statistical reports and field survey reports.These sets of data arecompiled and analyzed with such instruments as stereo viewers,transfer scopes ofvarious kinds,and mechanical and electronic planimeters.Calkins and Tomlinson(1977)point out that manual techniques could provide the same information ascomputer-aided techniques,and that the same processing sequences may occur.Whilethis may no longer be entirely true
