3 GIS Data Structure

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SPATIAL & NON-SPATIAL DATA

Spatial Data

Orientation of the object

Shape

Relative position with respect to other features More importantly, defined and described by

coordinates (x,y)

Non-Spatial Known as attribute data

Length, area, density, depth of soil, lithologies

In tabular form


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SPATIAL DATA: OBJECTS IN A MAP

Lithology map & landslides distribution


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NON-SPATIAL DATA: ATTRIBUTES

Also known as attributedata

Mainly tabular data

representing rows andcolumns

Rowsrepresentingindividual samplingpoints

Columnrepresentproperties/parameterfor the respectivesampling points


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RELATIONSHIP BETWEEN SPATIAL &

NON-SPATIAL DATA

Each object isidentified bydescriptions


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DATA STRUCTURE

Data Structure

Vector Raster

Line Point Polygon

Grid


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VECTOR STRUCTURE

Also known as spaghetti model

Presented as

a)Point

b)Linec)Polygon

All three structures (point, line, polygon) are basic

topological concept

Containing coordinates

Usually accompanied with non-spatial data

Ways of input includes digitizing using manual digitising

or on screen digitising (on the fly)


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VECTOR STRUCTURE: POINT

spatial object with no

area

geographicalrepresentation of

coordinates (lat, long)

wells, landslide locations,sampling stations, electric

pole

Landslide locations


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VECTOR STRUCTURE: LINE

connected sequenceof points

no area

the line itself is not acoordinate location,but coordinate/locationalong a line is definedat a specific point

Lineaments, roads,drainage line, contourlines

Drainage


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VECTOR STRUCTURE: POLYGON

A closed area

Usually divided into

different area

Land use,

geological map,

soil map

Soil map


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TOPOLOGY IN VECTOR DATA

The way in which features in GIS are connected toeach other

Spatial relationship between features (e.g. overlap,

adjacency, connectivity


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Entity Requirement

Point Geographical reference

Line Ordered set of points with define start

and end points which also give the line

direction

Area (polygon) How the line or point is connected to

define the boundary


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http://www.esri.com/news/arcnews/summer02articles/arcgis83-brings.html


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REPRESENTING VECTOR DATA

emyshoran.blogspot.com
http://www.google.com.my/url?sa=i&rct=j&q=vector+raster+data&source=images&cd=&cad=rja&docid=eHljywu8Q4RSiM&tbnid=tjGxi_QN-CYKkM:&ved=0CAQQjB0&url=http://emyshoran.blogspot.com/2012/06/geographic-information-system.html&ei=JmF_Ub6BAYa4rgfXjoAQ&psig=AFQjCNGokph6g-ShwybYqzy5F4ce-f30hw&ust=1367388714577269http://www.google.com.my/url?sa=i&rct=j&q=vector+raster+data&source=images&cd=&cad=rja&docid=eHljywu8Q4RSiM&tbnid=tjGxi_QN-CYKkM:&ved=0CAQQjB0&url=http://emyshoran.blogspot.com/2012/06/geographic-information-system.html&ei=JmF_Ub6BAYa4rgfXjoAQ&psig=AFQjCNGokph6g-ShwybYqzy5F4ce-f30hw&ust=1367388714577269


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RASTER DATA STRUCTURE

Continuous surface

Represented by pixels

Each pixel carries value

Slope angle map, slope

curvature map, elevation

map

Raster type elevation map


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TRANSFORMING VECTOR TO RASTER

Vector elevation data (contour) Raster elevation data

V t R t


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Vector on Raster


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www.automation-drive.com
http://www.google.com.my/url?sa=i&rct=j&q=vector+raster+data&source=images&cd=&cad=rja&docid=UyqMS-sE7oHb5M&tbnid=CeMzWPQeBmHJxM:&ved=0CAQQjB0&url=http://www.automation-drive.com/raster-data&ei=sWB_UZ3WLpHzrQeSgoGgBg&psig=AFQjCNGokph6g-ShwybYqzy5F4ce-f30hw&ust=1367388714577269http://www.google.com.my/url?sa=i&rct=j&q=vector+raster+data&source=images&cd=&cad=rja&docid=UyqMS-sE7oHb5M&tbnid=CeMzWPQeBmHJxM:&ved=0CAQQjB0&url=http://www.automation-drive.com/raster-data&ei=sWB_UZ3WLpHzrQeSgoGgBg&psig=AFQjCNGokph6g-ShwybYqzy5F4ce-f30hw&ust=1367388714577269http://www.google.com.my/url?sa=i&rct=j&q=vector+raster+data&source=images&cd=&cad=rja&docid=UyqMS-sE7oHb5M&tbnid=CeMzWPQeBmHJxM:&ved=0CAQQjB0&url=http://www.automation-drive.com/raster-data&ei=sWB_UZ3WLpHzrQeSgoGgBg&psig=AFQjCNGokph6g-ShwybYqzy5F4ce-f30hw&ust=1367388714577269http://www.google.com.my/url?sa=i&rct=j&q=vector+raster+data&source=images&cd=&cad=rja&docid=UyqMS-sE7oHb5M&tbnid=CeMzWPQeBmHJxM:&ved=0CAQQjB0&url=http://www.automation-drive.com/raster-data&ei=sWB_UZ3WLpHzrQeSgoGgBg&psig=AFQjCNGokph6g-ShwybYqzy5F4ce-f30hw&ust=1367388714577269


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ADVANTAGE: VECTOR & RASTER

Vector Raster

Good representation of the realworld

Compact data structure

Topology can be describedAccurate graphicsRetrieval, updating andgeneralisation of graphics andattributes are possible

graphic output is easy tovisualise

No data conversion is neededGeographic location of datacan be retained

Simple data structures Overlay /combination of data

with remotely sensed data is

easy Spatial analysis is easy Simulation is easy because of

the size and shape are thesame (pixel)

Good for continuous data (e.g.elevation, slope angle)


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DISADVANTAGE: VECTOR & RASTER

Vector Raster

Complex data structureOverlay of data is difficultAnalysis is difficultUnsuitable to representcontinuous data (e.g. elevation,slope angle)

Resolution problemUnsuitable to represent linear or curvylines

Choice of resolution and problem withgeneralisation occur when convertingvector to raster

High volumes of data (the higher theresolution, the more time it takes forprocessing)

Simplification of high volume data toreduce data size will involvegeneralisation

Not as beautiful as vector in terms ofpresentation

Network linkages is hard to establish


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DATA ERROR

Terminology:

a) Error: How far is the departure/difference from the real

value

b) Accuracy: The degree of the measured data close to its

true valuec) Precision: The level of detail. 160. 153m is more precise

than 160m

d) Bias: Consistency error

e) Resolution: How well the smallest feature can be

captured in the data

f) Generalisation: the degree of simplification when

handling the data

http://www.nuim.ie/staff/dpringle/gis/gis11.pdf


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SOURCES OF DATA ERROR

a) Data Input Error

I. Primary error

The original dataset such as a hardcopy map already containingerror, therefore the input data into the GIS system will also contain

this errorII. Secondary error

Refers to the errors that occurred during the process of entering thedata

b) Data Processing Error

Conversion of vector to raster. Converting vector to raster will resultin topological error. The real representation of vector will alsochange due to the selection of cell size in the conversion process.Small features may also lost due to cell size choices

http://www.nuim.ie/staff/dpringle/gis/gis11.pdf


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SOURCES OF DATA ERROR

c) Non-spatial errorRefers to attribute error where error occurred duringdescription/name/label were mistakenly entered by user

d) Conceptual errorRefers to how different people view the real world. For example,how do you view a building in GIS, a point or polygon

e) To err is human bionic eye shaky hand perception patience intelligence distraction-your phone?


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DATA ERROR EXAMPLE : SHRINK MAP

mappinglondon.co.uk
http://www.google.com.my/url?sa=i&rct=j&q=crumpled%20maps&source=images&cd=&cad=rja&docid=k6J8SZXpS5wwnM&tbnid=LHWaTg1pEZGrwM:&ved=0CAQQjB0&url=http://mappinglondon.co.uk/2011/the-crumpled-map-of-london/&ei=aS2QUaDKOMHUrQfNkoHoBg&psig=AFQjCNFzNrGku9ILfUZIZ2RIow87UUliBA&ust=1368489665849708http://www.google.com.my/url?sa=i&rct=j&q=crumpled%20maps&source=images&cd=&cad=rja&docid=k6J8SZXpS5wwnM&tbnid=LHWaTg1pEZGrwM:&ved=0CAQQjB0&url=http://mappinglondon.co.uk/2011/the-crumpled-map-of-london/&ei=aS2QUaDKOMHUrQfNkoHoBg&psig=AFQjCNFzNrGku9ILfUZIZ2RIow87UUliBA&ust=1368489665849708


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EXAMPLE DATA ERROR: CONVERSION

Rasterize

Vector Raster


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Rasterize

http://tutor.nmmu.ac.za/uniGISRegisteredArea/Material/Module%206/Adobe%20Files/C6%20Section02.pdf


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Elevation in raster Contour lines

generated from raster

Original contour

lines


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Point? Polygon?

How do you

perceive a

feature


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2 lines? 1 line?

How do you

perceive a

feature


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REFERENCES

Advantage & Disadvantage of Data structure

http://planet.botany.uwc.ac.za/nisl/GIS/GIS_primer/page_19.htm

Chandra, A.M. & Ghosh, S.K. 2006. Remote Sensing andgeographical information system. Alpha Science: Oxford

Bonham-Carter, G.F. 1994. Geographic InformationSystems for Geoscientists: Modelling with GIS. Ontario:Pergamon

Burrough, P.A. 1991. Principles of GeographicalInformation Systems for Land Resources Assessment.Oxford: Calendron Press

i t l i l ti l
http://planet.botany.uwc.ac.za/nisl/GIS/GIS_primer/page_19.htmhttp://planet.botany.uwc.ac.za/nisl/GIS/GIS_primer/page_19.htmhttp://planet.botany.uwc.ac.za/nisl/GIS/GIS_primer/page_19.htmhttp://planet.botany.uwc.ac.za/nisl/GIS/GIS_primer/page_19.htmhttp://planet.botany.uwc.ac.za/nisl/GIS/GIS_primer/page_19.htm

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3 GIS Data Structure