spatial data acquisition – specific theory

8/17/2019 Spatial Data Acquisition – Specific Theory

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GISWEB: Department of Geomatics, The University of Melbourne

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Spatial Data Acquisition – Specific Theory

This theory section ill !escribe the operations re"uire! to create both a raster #cell$base!% an!

vector GIS !atabase from various input sources& These 'ey functions ill intro!uce theconcepts of cell si(es, resolution an! scale an! lin' these to the future mo!ellin) an! analysisre"uirements of a GIS&

Introduction

Data input is the operation of enco!in) !ata for inclusion into a !atabase& The creation ofaccurate !atabases is a very important part of GIS&

Data collection, an! the maintenance of !atabases, remains the most e*pensive an! timeconsumin) aspect of settin) up a ma+or GIS facility& This typically costs -$.-/ of the overallcosts of a GIS pro+ect&

There are a number of issues hich arise hen !evelopin) a !ata base for a plannin) ormana)ement pro+ects& The first issue is shoul! the !ata be store! in vector or raster format&0onsi!erations here inclu!e:

o the nature of the source !ata e&)& it is alrea!y in raster formo the pre!ominant use to hich it ill be puto the potential losses that may occur in transitiono stora)e space #increasin)ly less important%o re"uirements for !ata sharin) ith other systems1softare

2s a )eneral rule it is best to retain the ma*imum amount of information in the !ata base& If the!ata is available as points, lines or poly)ons then it shoul! be 'ept that ay& If a rasterappro*imation of this !ata is also nee!e! for analytical purposes then a raster version of the!ata may be 'ept in a!!ition to the vector covera)e& Many systems provi!e from "uic'conversion from vector to raster&

The issue of scale is often raise! in relation to GIS !ata base !evelopment& It is important toremember that !ata store! in a GIS !oes not have a scale& Sometime people refer to a 3:45---scale !ata base& What they mean is that the !ata has been ta'en from 3:45--- maps or that ithas a level of accuracy hich is rou)hly e"uivalent to that foun! on 3:45--- scale maps&

In line ith the principle of 'eepin) the most information possible the i!eal is to fill the !ata baseith !ata ith accuracies e"uivalent to very lar)e scale maps& This hoever may not alays bepractical as:

o the !ata may not be available at very lar)e scale,o it may be too e*pensive or time consumin) to !i)itise from that scale,o there may be no envisione! application that re"uires that accuracy6

so compromises are ma!e&

7roblems can arise hen some of the !ata in a GIS is very accurate #!ran from lar)e scalemappin) 8 e&)& urban utilities% an! other !ata is !ran from much smaller scale mappin) #e&)&soils%& In this case )reat care has to be ta'en that conclusions are not !ran on the basis of theless reliable !ata&

There are several metho!s use! for enterin) spatial !ata into a GIS, inclu!in):o manual !i)itisin) an! scannin) of analo)ue mapso ima)e !ata input an! conversion to a GISo !irect !ata entry inclu!in) )lobal positionin) systems #G7S%o transfer of !ata from e*istin) !i)ital sourceso maps: scale, resolution, accuracy

2t each sta)e of !ata input there shoul! be !ata verification shoul! occur to ensure that the

resultin) !atabase is as error free as possible&


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When !evelopin) a raster !ata set for specific purposes there are a number of !esi)nconsi!erations& These inclu!e: the physical e*tent of the !ata base6 the resolution #)ri! si(e%6the themes to be inclu!e!6 the classifications to be use! ithin the themes, an! theappropriateness of scale of input !ata to the preferre! )ri! si(e&

Physical ExtentShoul! the !ata base cover only the area bein) planne! or mana)e!9 ; 2re there e*ternalinfluences #upstream catchment, ma+or transport corri!ors, nearby population centres, vies toa!+acent scenery% hich nee! to be incorporate! as part of the plannin) !ata&

ResolutionThe hi)her the resolution the better the appro*imation of reality $ provi!e! the !ata is )oo!enou)h to support this resolution& If you assume a certain error in map preparation an!!i)itisation then this translates to a certain on )roun! error& There is little point in ma'in) the)ri! si(e smaller than the probable error& 2 smaller than necessary )ri! si(e lea!s to lar)er filesan! lon)er processin) times& In the best case halvin) the cell si(e ill "ua!ruple the processin)time& E*perience ith raster processin) su))ests that more than 4 million cells is e*cessive inmost conte*ts& i)ures 3 an! 4%& The resolution of coor!inate !ata is !epen!ent on mo!e of !i)iti(in):

In point$mo!e the !i)iti(in) operator specifically selects an! enco!es those points !eeme!


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$i"ure 1 Point%mode di"itisin"

$i"ure 2 &tream%mode di"itisin"

n$screen !i)itisin) is an interactive process in hich a map is create! usin) previously

!i)itise! of scanne! information& This metho! of )eoco!in) is commonly calle!

Di)itisin) errors ill alays occur #un!ershoots, overshoots, trian)les%&

E!itin) of !i)itise! features involves error correction, enterin) missin) !ata, formin) topolo)y&

There are many issues to consi!er before !i)itisin) commences, inclu!in) #McGoan, 3==.%:o >or hat purpose ill the !ata be use!9o What coor!inate system ill be use! for the pro+ecto What is the accuracy of the layers to be associate!9 If it is si)nificantly !ifferent, the

layers may not match&o What is the accuracy of the map bein) use!9o Each time you !i)itise, !i)itise as much as possible& This ill ma'e your techni"ue

more consistent& >or more consistency, only one person shoul! or' on a )iven!i)itisin) pro+ect&

o If the source consists of multiple maps, select common reference points that coinci!e

on all connectin) sheets& >ailure to !o this coul! result in !i)itise! !ata from !ifferent!ata sheets not matchin)&

o If possible, inclu!e attributes hile !i)itisin), as this ill save time later&o Will it be mer)e! ith a lar)er !atabase9

!a# re"istration or 'eoreferencin"

;e)istration of the map nee!s to be performe! for each ne !i)iti(in) session, as ell as eachtime the map@s position is chan)e! on the !i)iti(er #see >i)ure A%&

This is so that the coor!inates of the !i)itiser can be converte! into )eo)raphic coor!inates&The !i)itisin) pro)ram ill re"uire the map scale, an! the )eo)raphic coor!inates of the controlpoints hich ill be use!& These control points shoul! )enerally be ell space!, for e*amplenear the corners of the map& Depen!in) on the softare bein) use! a minimum of four pointsare re"uire!& These locations of these points then nee! to be !i)itise!&

2lays use the same control points for each session of a particular map sheet&


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Figure 3 The digitiser table and puck

Some softare may re"uire the establishment of the si(e of the !i)iti(in) in!o by clic'in) in

the loer left corner an! upper left corner of the re)ion of interest&

2n error limit nee!s to be specifie!& This is the ma*imum error that is acceptable to re)ister your paper map& The !efault error limit is -&-- inches #or its e"uivalent units%& nce you enter aminimum of pairs of map an! paper control points, 2rcCie calculates the ;oot Mean S"uare#;MS% error an! compares the value ith the one you specifie! in the Error imit e!it bo*& If thecalculate! error is less than the specifie! error limit, ;e)ister button is enable! for you tore)ister the map&

R!& error

The ;oot Mean S"uare #;MS% error represents the !ifference beteen the ori)inal controlpoints an! the ne control point locations calculate! by the transformation process& Thetransformation scale in!icates ho much the map bein) !i)itise! ill be scale! to match the

real$orl! coor!inates&The ;MS error is )iven in both pa)e units an! in map units& To maintain hi)hly accurate)eo)raphic !ata, the ;MS error shoul! be 'ept un!er -&-- inches #or its e"uivalentmeasurement in the coor!inate system bein) use!%& >or less accurate !ata, the value can be ashi)h as -&--. inches or its e"uivalent measure&

0ommon causes of hi)h ;MS error are $ incorrectly !i)itise! control points, careless placementof control points on the map sheet, an! !i)itisin) from a rin'le! map& >or more accurateresults hen !i)itisin) a control point, chec' that the crosshairs of the !i)itiser puc' remaincentere! on the control point&

Scanning

2nother approach is to use a scanner to convert the analo)ue map into a computer$rea!ableform automatically& ne metho! of scannin) is to recor! !ata in narro strips across the !atasurface, resultin) in a raster format& ther scanners can scan lines by folloin) them !irectly&

Maps are often scanne! in or!er to:o Use !i)ital ima)e !ata as a bac')roun! for other #vector% map !atao 0onvert scanne! !ata to vector !ata for use in a vector GIS

Scannin) re"uires that the map scanne! be of hi)h carto)raphic "uality, ith clearly !efine!lines, te*t an! symbols6 be clean an! have lines of -&3mm i!th or i!er&

Scannin) comprises to operations:o scannin), hich pro!uces a re)ular )ri! of pi*els ith )rey$scale levels #usually in the

ran)e -$455%o binary enco!in) 8 to separate the lines from the bac')roun! usin) automate! feature

reco)nition techni"ues


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E!itin) of scanne! !ata can inclu!e: pattern reco)nition of shapes an! symbol can!i!ates6 linethinnin) an! vectorisation6 error correction6 supplementin) missin) !ata, an! formin) topolo)y&

See Berhar!sen #3==4% for more !etail&

*irect data entry

Surveying and manual coordinate entry

o In surveyin), measure! an)les an! !istances from 'non points are use! to

!etermine the position of other pointso Surveyin) fiel! !ata are almost alays recor!e! as polar coor!inates an!

transforme! into rectan)ular coor!inates

Surveyin) fiel! !ata are almost alays recor!e! as polar coor!inates an! transforme! intorectan)ular coor!inates& 7olar coor!inates are compose! of: a measure! !istance an! an an)lemeasure! cloc'ise from ?orth&

Global positioning systems (GPS)

2 Global 7ositionin) System #G7S% is a set of har!are an! softare !esi)ne! to !etermineaccurate locations on the earth usin) si)nals receive! from selecte! satellites& ocation !ataan! associate! attribute !ata can be transferre! to mappin) an! Geo)raphical InformationSystems #GIS%& G7S ill collect in!ivi!ual points, lines an! areas in any combination necessaryfor a mappin) or GIS pro+ect& More importantly, ith G7S you can create comple* !ata!ictionaries to accurately an! efficiently collect attribute !ata& This ma'es G7S is a veryeffective tool for simultaneously collectin) spatial an! attribute !ata for use ith GIS& G7S isalso an effective tool for collectin) control points for use in re)isterin) base maps hen 'nonpoints are not available&

G7S operate by measurin) the !istances from multiple satellites orbitin) the Earth to computethe *, y an! ( coor!inates of the location of a G7S receiver&

The folloin) forms of G7S e"uipment are currently available to users:o Small han!$hel! unitso Fames Bon!$type ristatch unitso In$car navi)ation systemso Bac'$pac' unitso 2ircraft an! ship mounte! systemso Belt$mounte! units hich can be lin'e! !irectly to earable computers containin)

GIS !atabaseso Mobile telephone installe! units

+ses of 'P&

G7S can be use! for )eoreferencin), positionin), navi)ation, an! for time an! fre"uencycontrol& G7S is increasin)ly use! as an input for Geo)raphic Information Systems particularly

for precise positionin) of )eospatial !ata an! the collection of !ata in the fiel!&

The system

The system har!are contains three parts6 the antenna, the receiver, an! the !atalo))er6sometimes calle! a !ata$collector&

The !atalo))er is a han!$hel! computer that contains softare to coor!inate si)nal collectionan! stora)e, file manipulation, an! file transfer to an! from a computer& Some systems mi)htcombine some of these elements into a sin)le piece of har!are&

The system softare, hich normally resi!es on a computer, has four primary functions:preplannin), post$processin) correction of the ra satellite !ata, !isplay1e!itin) of the !ata, an!convertin)1e*portin) of the !ata& 7replannin) inclu!es !eterminin) satellite availability for aparticular place an! time, an! the preparation of !ata !ictionaries for a particular +ob& 0orrectioninvolves the use of a base station file to apply corrections to the ra !ata collecte! from thesatellites, )reatly improvin) accuracy&


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E!itin) an! !isplay can inclu!e avera)in) points, connectin) points to form lines or areas,smoothin), measurin) !istance an! area, an! !isplayin) the !ata to screen& G7S softarepro)rams are not meant to be map$ma'in) pro)rams an! usually most of the final e!itin) illta'e place in a GIS pro)ram&

Data conversion an! e*port inclu!e the capability to convert from the sphericalatitu!e1on)itu!e #at1on)% coor!inates that the receiver collects into a variety of othercoor!inate systems an! !atums, an! then e*portin) this !ata in a variety of formats use! by!ifferent 02DD an! GIS pro)rams&

The satellites

The 'non !istances an! locations of each visible satellite are use! to locate the position of thereceiver& We can place ourselves anyhere on a sphere aroun! one satellite once e 'no the!istance to the satellite& non !istances from to satellites ill place us on a circle that is theintersection of to spheres& non !istances from three satellites ill place us in to points,hich is the intersection of three spheres& We may be able to eliminate one of these points asbein) impractical, such as out in space or !eep un!er)roun!& With one )one, the other must becorrect& Three satellites are sufficient, at least theoretically, to provi!e receiver location& More

satellites simply a!! confirmation to the receiver location& In practice, the more satellites thebetter& >our satellites are the minimum to secure only one, absolutely technically,tri)onometrically unambi)uous location& Three or' in practice since e can eliminate theabsur! location&

>our satellites #normal navi)ation% can be use! to !etermine three position !imensions an!time& Hoever user mista'es, inclu!in) incorrect )eo!etic !atum selection, can cause errorsfrom 3 to hun!re!s of meters& ;eceiver errors from softare or har!are failures can alsocause errors of any si(e&

G7S satellite si)nals are bloc'e! by most materials& G7S si)nals ill not mass throu)hbuil!in)s, metal, mountains, or trees& eaves an! +un)le canopy can attenuate G7S si)nals sothat they become unusable& In locations here at least four satellite si)nals ith )oo! )eometrycannot be trac'e! ith sufficient accuracy, G7S is unusable& 7lannin) softare may in!icate

that a location ill have )oo! satellite covera)e over a particular perio!, but terrain, buil!in), orother obstructions may prevent trac'in) of the re"uire! satellites&

The G7S satellites circle the earth tice a !ay, 3-,=-- miles above the earth& There are 4satellites in the G7S constellation& Tenty$one satellites can be calle! on at any time6 the otherthree are spares in case one of the others becomes unhealthy&

>ive or si* satellites are above an! visible #by ra!io ave% to any spot on the earth at any onetime& Buil!in)s, hills, trees, an! other )roun! features may bloc' one or more at one time, orone or to of the satellites may not be at their best& These problems ill re!uce the number ofuseful satellites above a position to to, an! maybe even one, but three or four are commonlyavailable& ften as many as five an! si* are visible&

The location in space of each satellite is 'non& The orbits are carefully planne! an! constantly

up!ate! so that actual location is never off by much from the inten!e! location& Each satelliteconstantly announces its number, an! the time that si)nal as sent&

The !istance from each satellite to the receiver is calculate! by comparin) the time the si)nalsays it as sent ith the time the receiver pic's up the si)nal& The time !ifference is multiplie!by the spee! of li)ht to )et the !istance from satellite to receiver& This is !one for each satellitethe receiver can


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Figure 4 Differential GPS

Ima"e data in#ut and con/ersion to a 'I&

Ima)e !ata inclu!es satellite ima)es, aerial photo)raphs an! other remotely sense! or scanne!!ata& Ima)e !ata is in a raster !ata& Each )ri!$cell, or pi*el, has a certain value !epen!in) onho the ima)e as capture! an! hat it represents& >or e*ample, if the ima)e is a remotelysense! satellite ima)e, each pi*el represents li)ht ener)y reflecte! from a portion of the Earthssurface&

Remote Sensing

;emote sensin) inclu!es all information collecte! from sensors hich are physically separatefrom the ob+ect& In the conte*t of this thesis, remote sensin) is concerne! ith !erivin)information about the Earths surface usin) an elevate! platform, to pro!uce such informationas satellite !ata or aerial photo)raphy&


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Figure 5 Part of a satellite image

;emote sensin) instruments rely upon the !etection of ener)y emitte! from, or reflecte! by, theob+ect un!er consi!eration& ;emote sensin) allos the measurement an! monitorin) of surfaceelectroma)netic variation, an! as such this !ata provi!es a uni"ue ay of viein) thelan!scape& Satellite remote sensin) is the only source of !ata ith hich e can vie the entireplanet an! monitor the chan)e in the nature of the surface of the planet throu)h time, in aconsistent, inte)rate!, synoptic an! numerical manner&

Satellite remote sensin) has the ability to provi!e complete, cost$effective, repetitive spatial an!temporal !ata covera)e, hich means that various phenomena can be analyse! synoptically,an! such tas's as the assessment an! monitorin) of lan! con!ition can be carrie! out overlar)e re)ions&

2s ell as bein) of use by itself, remote sensin) can be also be use! as an important !atasource for the !evelopment an! refinement of mo!els, an! can be use! to vali!ate mo!els&

When usin) satellite remote sensin), the relationship beteen spectral response an! )roun!features is complicate! by the fact that in!ivi!ual ima)e cells #pi*els%, hich can ran)e from 3-m to 3 'm in si(e !epen!in) on the source of !ata use!, are hetero)eneous an! may contain ami*ture of phenomena #see >i)ure 5 belo%& The in!ivi!ual spectral responses of featuresithin a cell are avera)e! to pro!uce the value for the cell& Therefore, metho!s of remotesensin) ill only be effective if the phenomena, or classes of the phenomena, cover areas

lar)er than a pi*el&


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$i"ure ) Classification errors occur hen the sie of the "rid cell s lar"er than the features hichare 4ein" ma##ed ,after 5urrou"h 16 $i"ure 6.3 #.112-

Therefore the spectral !ata nee!s to be enhances, filtere! or perhaps )eometrically transforme!ith ima)e processin) techni"ues before it can incorporate! into a GIS& 2n important problem isthe rectification of the remotely sense! ima)ery ith the )ri! hich the GIS is usin)&

;ectification is the process by hich an! ima)e or )ri! is converte! form ima)e coor!inate! toreal$orl! coor!inates& ;ectification typically involves rotation an! scalin) of )ri! cells an! thusre"uires resamplin) of values& This is achieve! by usin) resamplin) techni"ues hich involve!efinin) ne pi*el positions for the GIS map )ri!, an! fillin) them ith !ata !etermine! byinterpolation al)orithms such as nearest nei)hbour, bilinear interpolation or cubic convolution#see the ;aster Spatial 2nalysis Mo!ule for more information on spatial resamplin)%&

Aerial photographs, air photo interpretation and digital photogrammetric

mapping

2erial photo)raphic interpretation has been the most i!ely use! form of remote sensin) forenvironmental applications to !ate, ith techni"ues bein) ell establishe!& This i!e use stemsfrom the availability of aerial photo)raphs, an! the fact that they can provi!e very hi)h spatialresolution !ata, !on to metre accuracy, not historically available from other sensors&

ualitative analysis relies on ima)e interpretation an! is basically !escriptive& 7hotointerpretation involves a human analyst viein) an ima)e, an! e*tractin) information, an! !ueto its use of the human min!, is une"ualle! in the possibilities of pattern reco)nition an! spatialassociation& The success of this techni"ue is hi)hly !epen!ent on the analyst effectivelye*ploitin) the spatial, spectral an! temporal elements present in the ima)e& Ima)es, hetheraerial photo)raphs or satellite ima)ery, have a very hi)h !escriptive value !ue to the ability of

the human interpreter to interpolate an! fin! patterns&>or both aerial photo)raphs an! space$borne remotely sense! !ata, the scale of the ima)e ill!etermine to a lar)e e*tent the potential of the interpretation&

7hoto interpretation, hether of aerial photo)raphy or of satellite remote sensin) !ata, is proneto the problems of bein) non$repeatable an! not offerin) uniformity of analysis& It is hi)hlysub+ective an! !epen!s upon the interpreter@s 'nole!)e an! un!erstan!in) of the spatial areaun!er consi!eration an! the process or phenomena involve!&

o The combination of aerial photo)raphy an! air photo interpretation provi!esinformation on relatively lar)e areas ithout inspection of the )roun!

o ;oa!s, la'es an! ater bo!ies, buil!in), farmlan! an! forests are clearly visible on

aerial photo)raphso ther characteristics such as ve)etation, soil an! )eolo)ical formations are more

!ifficult to interpret, hoever s'ille! an! e*perience! interpreters can e*tract a )reatamount of useful information from aerial photo)raphy


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o Usin) air photo interpretation, the aerial photo)raph is classifie! by the interpreter,

ith the !ata bein) then input into a !atabase or is use! for the up!atin) ofpreviously hel! information

$i"ure 6 erial Photo Inter#retation of an ima"e into classes ,Cam#4ell 13-


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Di)ital photo)rammetric mappin) uses !i)ital ima)es of a pair of overlappin) photo)raphs an!operators use special AD )lasses to !i)itise #*, y, (% coor!inates of features&

$i"ure 7 $li"ht #ath for aerial #hoto"ra#hy shon a4o/e here the hole area is co/ered 4yaerial #hoto"ra#hs usually ith a 60 o/erla# alon" each fli"ht line and a 20 o/erla# 4eteenfli"ht lines. The loer #art of the ima"e shos the idea 4ehind the use of a #air of stereo ima"esfor stereo%#lottin" or ima"e inter#retation.

Transfer data from existin" di"ital sources

2 chan)e is occurrin) in the transformation !ata into a GIS !atabase& ri)inally most of the !ataas !erive! from !i)itisin) analo)ue maps, or from !irect !ata entry& ?o a lar)e amount ofinformation is no !istribute! in !i)ital formats, so there is a i!er use of e*istin) !i)italsources&

The !i)ital !ata Jrevolution@ also means that users must often search for materials in !ifferentplaces& To ac"uire some !i)ital sources, users must contact the pro!ucers !irectly to )ain thenecessary !ata in a compatible format& Such !ata can be obtaine! from Government 2)enciessuch as 2ustralian Geolo)ical Survey r)anisation http:11&a)so&)ov&au , the 2ustralianSurvey an! an! Information Group #2USIG% http:11&ausli)&)ov&au , an! other sources&

The Internet an! Worl!i!e Web are bein) use! to !istribute !ata to a )reater e*tent by manyor)ani(ations an! a)encies& The US >e!eral Geo)raphic Data 0ommittees eb pa)e athttp:11&f)!c&)ov has the US ?ational Geospatial Data 0learin)house containin) lin's tohun!re!s of or)anisations that maintain an! provi!e GIS !ata, both in the US an! aroun! theorl!& In some cases, you can !onloa! the !ata !irectly an! use it in 2rcCie&

http://www.agso.gov.au/http://www.auslig.gov.au/http://www.fgdc.gov/http://www.agso.gov.au/http://www.auslig.gov.au/http://www.fgdc.gov/


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ES;Is eb pa)e #http:11&esri&com% also contains lin's to or)ani(ations that maintain an!provi!e GIS !ata& >rom the eb pa)e you can chec' out the Data Houn!: its a )oo! place tostart your "uest for !ata& The Data Houn! offers lin's to other GIS sites that offer free,!onloa!able !ata&

The real problem at the local an! state levels is that )overnment a)encies or)ani(ethemselves$$an! their !ata$$in very !ifferent ays from place to place& Because states an! citiesvary so )reatly in their systems of or)ani(ation, it sometimes ta'es time to !iscover hicha)ency hol!s the information you ant& In some cases, states an! cities are re"uire! to collectcertain types of information to comply ith fe!eral an! state re)ulationsKbut a)ain thea)encies that actually compile this information may vary from place to place&

The issue then becomes one of transferrin) the !ata from the supplie! format into that nee!e!&

When GIS first be)an to appear, users either !evelope! their on formats for storin) spatialinformation or employe! those !efine! by !ata hol!ers an! their softare&

The formats ere often specific to the nee!s of particular pro+ects an! ere not inten!e! tomeet the nee!s of a broa!er ran)e of users& It as often very !ifficult to share an! transfer !ata&

Users reco)ni(e! that much time an! money as bein) aste! hen !atasets coul! not beshare! amon) a broa!er clientele&

The Unite! States Geolo)ical Survey #USGS% as one of the first a)encies to be)ine*perimentin) ith !ata formats that coul! serve both their nee!s an! those of a i!er public&The USGSs !i)ital line )raphs #DG% as the result, althou)h both of these early formats havesince been further refine! into the DG$4 format& The DGs ere a ay of co!in) information!ran from the USGSs conventional paper "ua!ran)le sheet maps&

The !evelopment of stan!ar!s an! the proliferation of conversion an! translation softare hasha! a )alvani(in) effect on the GIS orl!& Where once users ha! to count on !i)iti(in) !atasetsfrom scratch, they can no use a i!e ran)e of publicly available files& The )roth in availablefiles has been hu)e& The emer)ence of ne !ata transfer stan!ar!s may increase the pace of!evelopment further&

0ommon !ata transfer formats inclu!e:o 2ustralian Spatial Data Transfer Stan!ar! #SDTS%o DL> #Drain) E*chan)e >ile%o F7EG fileso C7> #Cector 7ro!uct >ormat !ata

Most GIS pac'a)es no contain a suite of softare al)orithms that ill perform the necessary!ata transfers&

The !ata obtaine! from other sources shoul! contain meta$!ata, that is !ata about the !ata, ora sort of

If !ocumentation is limite!, it is important for you to consi!er the folloin) "uestions:o What is the a)e of the !ata9o Where !i! it come from9o In hat me!ium as it ori)inally pro!uce!9o What is the areal covera)e of the !ata9o To hat map scale as the !ata !i)iti(e!9o What pro+ection, coor!inate system, an! !atum ere use! in maps9o What as the !ensity of observations use! for its compilation9o Ho accurate are positional an! attribute features9o Does the !ata seem lo)ical an! consistent9o Is the !ata relevant to the pro+ect at han!9o In hat format is the !ata 'ept9o Ho as the !ata chec'e!9o Why as the !ata compile!9


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o What is the reliability of the provi!er9

!a#s

map scale

Map scale is the relationship e*istence beteen !istance on a map an! the correspon!in)!istance on the earth& It is usually e*presse! in the folloin) form: 3:3-,---, meanin) that 3 unitof measurement on the map represents 3-,--- of the same units on the earth@s surface& Thescale ratio 3:3--,--- means that one unit of !istance on the map represents 3--,--- of thesame units of !istance on the Earth& So on a 3:3--,--- scale map, one cm on the map e"ualsone 'm on the )roun! because one 'm has 3--,--- cm& Because the scale ratio is a constant,it is true for hatever units in hich the fraction is e*presse!&

2 Jlar)e@ scale map is one in hich a )iven part of the Earth is represente! by a lar)e area onthe map& ar)e scale maps )enerally sho more !etail than small scale maps because at alar)e scale there is more space on the map in hich to sho features& ar)e scale maps aretypically use! to sho site plans, local areas, nei)hborhoo!s, tons etc& 3:4,5-- is an e*ample

of a lar)e scale& 2 Jsmall@ scale map is one in hich a )iven part of the Earth is represente! by a small area onthe map& Small scale maps )enerally sho less !etail than lar)e scale maps, but cover lar)eparts of the Earth& Maps ith re)ional, national, an! international e*tents typically have smallscales, such as 3:3,---,---& ar)e scale maps typically sho more !etail than small scalemaps, hereas on smaller scale maps there is simply not enou)h room to sho all the available!etail, so features such as streams an! roa!s often have to be represente! as sin)le lines, an!area features li'e cities, have to be shon as points& This is calle! )enerali(ation&

The lar)er a scale is the smaller ill be the number in the scale& >or e*ample, a 3:3-,---$scalemap is sai! to have a lar)er scale than a 3:3--,---$scale map&

Map projections

Map pro+ections are a mathematical mo!el for convertin) locations on the earth@s surface fromspherical to planar coor!inates, alloin) flat maps to !epict three$!imensional features& Somemap pro+ections preserve the inte)rity of shape, others preserve accuracy of area, !istance or!irection& 2ll map pro+ections !istort shape, area, !istance or !irection to some e*tent&

n lar)e scale maps, such as street maps, the !istortion cause! by the map pro+ection bein)use! may be ne)li)ible because your map ill typically cover only a small part of the Earthssurface&

n smaller scale maps, such as re)ional an! orl! maps, here a small !istance on the mapmay represent a consi!erable !istance on the Earth, this !istortion may have a bi))er impact,especially if the application involves comparison of the shape, area or !istance of !ifferentfeatures& In these cases, 'nole!)e of the characteristics of the map pro+ection you are usin)becomes more important&

Map detail

It is natural to e"uate !etail ith accuracy& Hoever, hen e tal' about the level of !etail on amap, e are referrin) to the "uantity of )eo)raphic information shon& Map accuracy, on theother han!, is a statement of the "uality of this information&

While lar)e scale maps typically sho more !etail than small scale maps, there is no stan!ar!rule for ho many features a map of a )iven scale can sho, an! in ho much !etail& Instea!,this is a carto)raphic !ecision !epen!in) on the purpose of the map an! ho many symbolscan be !ran in the available space ithout visual clutter&

n smaller scale maps there is simply not enou)h room to sho all the available !etail, sofeatures such as streams an! roa!s often have to be represente! as sin)le lines, an! area

features li'e cities, have to be shon as points& This is calle! )eneralisation&


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When features are )eneralise! their level of !etail is re!uce! to avoi! clutterin) the map, buttheir overall shape an! position is retaine!& Therefore, a small scale map of a coastline ill notsho every cove that you mi)ht see on a lar)e scale map& Smaller scale maps may also omitfeatures completely&

In some GIS pac'a)es spatial !ata can be )enerali(e! after it has been create!& 2;01I?> hasfunctions for automatically )enerali(in) e*istin) spatial !ata by removin) coor!inates&

Map accuracy

The accuracy of a map is not !epen!ent on the maps scale& Instea!, it !epen!s on theaccuracy of the ori)inal !ata use! to compile the map, ho accurately this source !ata hasbeen transferre! onto the map, an! the resolution at hich the map is printe! or !isplaye!&

The accuracy of the maps you create ith 2rcCie !epen!s primarily on the "uality of thecoor!inate !ata in your spatial !atabase& To create the spatial !ata, e*istin) maps ormanuscripts may have been !i)iti(e! or scanne!, an! other ori)inal !ata, such as surveyreports, aerial photo)raphs an! ima)es, an! !ata from thir! parties may also have been use!&our final map ill therefore reflect the accuracy of these ori)inal sources&

2s scales become smaller, one unit of map !istance represents a lar)er !istance on the )roun!&So if one of the features shon on a very small scale map is out of line by +ust a part of amillimeter, it oul! still represent a substantial inaccuracy in reality&

Map resolution

Map resolution is !efine! as:o the si(e of the smallest feature that can be represente! in a surface&o the accuracy at hich the location an! shape of map features can be !epicte! for a

)iven map scale& In a lar)e scale map #e&)& a map scale of 3:3% there is less re!uctionof features than those shon on a small scale map #e&)& 3:3,---,---%& n a lar)erscale map feature resolution more closely resembles real$orl! features& 2s mapscale !ecreases, resolution also !iminishes as feature boun!aries must be

smoothe!, simplifie! or not shon at all #Berry, 3==5%&

References

Bernhar!sen, T& #3==4% Geo)raphic Information Systems& Cia' IT1?ore)ian Mappin) 2uthority, 2ren!al, ?oray&

Benrhar!sen, T& #3==% Geo)raphic Information Systems& Halste! 7ress&

Bernhar!sen, T& #3===% Geo)raphic information systems : an intro!uction& Wiley, ?e or'&

Berry, F&& #3==5% Beyond Mapping: Concepts, Algorithms and Issues in GIS& GIS Worl! Boo's,>ort 0ollins, US2&&

Burrou)h, 7&2& #3=.% Principles of Geographic Information Systems for Land Resource

Assessment & Mono)raphs on Soil an! ;esources Survey ?o& 34, *for! Science 7ublications,?e or'&

0ampbell F&B& #3=.A% Mapping the Land: aerial imagery for land use information& ;esource7ublications in Geo)raphy, 2ssociation of 2merican Geo)raphers, Washin)ton D&0&

0urran, 7&F& #3=.5% Principles of Remote Sensing & on)man Scientific an! Technical Group,Esse*, En)lan!&

Dana, 7&H& #3==N% Gloal Positioning System !"er"ie# & ?0GI2 0ore 0urriculum in GIScience,U;: http:11&nc)ia&ucsb&e!u1)iscc1units1u-3N1u-3N&html&

Environmental Systems ;esearch Institute #ES;I% #3==% $or%ing #ith the Arc&ie# Spatial Analyst &

>oote, &E& an! ynch, M& #3==5% Database 0oncepts& The Geo)raphers 0raft 7ro+ect,Department of Geo)raphy, The University of 0olora!o at Boul!er& U;:http:11&colora!o&e!u1)eo)raphy1)craft1notes1sources1sourcesOf&html


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Goo!chil!, M& #3==N% Rasters& ?0GI2 0ore 0urriculum in Geo)raphic Information Science& Unit-55, U;: http:11&nc)ia&ucsb&e!u1)iscc1units1u-551u-55&html&

Harrison, B&2& an! Fupp, D&B&& #3=.=% Introduction to Remotely Sensed 'ata: Part !ne of themicroBRIA( Resource Manual , 0SI; 7ublications, Melbourne&

Hobbs, ;&F&, Wallace, F&>& an! 0ampbell, ?&2& #3=.=% 0lassification of ve)etation in the Western 2ustralian heatbelt usin) an!sat MSS !ata& &egetatio .-, =3$3-5&

Hunter, G&F& #4---% 'ata Ac)uisition& ecture ?otes, 53$A34 GIS an! ;emote Sensin) forEnvironmental Science, Department of Geomatics, University of Melbourne&

Fohnston, ;&M& an! Barson, M&M& #3==-% An Assessment of the use of Remote Sensing*echni)ues in Land 'egradation Studies& Bureau of ;ural ;esources, Bulletin ?o& 5, 2ustralianGovernment 7ublishin) Service, 0anberra&

McGoan, E& #3==.% Planning a digitising pro+ect & The ?0GI2 GIS 0ore 0urriculum forTechnical 7ro)rams& Unit 34& U;: http:11&nc)ia&ucsb&e!u1cctp

7ioar, F&M& an! eDre, E&>& #3==5% Hypertemporal analysis of remotely sense! sea$ice !ata

for climate chan)e stu!ies& Progress in Physical Geography 3=#4%, 43$44&uattrochi, D&2& an! 7elletier, ;&E& #3==-% ;emote sensin) for analysis of lan!scapes: anintro!uction& In: Turner, M&G& an! Gar!ner, ;&H& #e!s&% uantitati"e Methods in Landscape-cology: the analysis and interpretation of landscape heterogeneity & Sprin)er$Cerla), ?e or',53$N&

;ichar!s, F&2& #3=.% Remote Sensing 'igital Image Analysis: an introduction, Sprin)er$Cerla),Berlin&

Schaeffer, F& #3==.% Usin) G7S Data& The ?0GI2 GIS 0ore 0urriculum for Technical 7ro)rams&Unit 4& U;: http:11&nc)ia&ucsb&e!u1cctp

Tomlin, 0&D& #3==-% Geographic Information Systems and Cartographic Modelling & 7rentice Hall,?e Fersey&

Trimble ?avi)ation imite! #4---% eb site http:11&trimble&com1
http://www.trimble.com/http://www.trimble.com/

spatial data acquisition – specific theory

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