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Transcript of COMPUTERS AND STATISTICS IN ARCHAEOLOGY Week 4. Geographic Information Systems (GIS) - 2 © Richard...
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COMPUTERS AND COMPUTERS AND STATISTICS IN STATISTICS IN
ARCHAEOLOGYARCHAEOLOGY
Week 4. Geographic Week 4. Geographic Information Systems (GIS) - 2Information Systems (GIS) - 2
© Richard Haddlesey www.medievalarchitecture.net
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Aims WEEK 4 Examine the differences between vector and raster graphics Discuss which data types are best represented by each Examine how ArcGIS treats vector graphics Outline vector data sources Create new vector themes by digitising in ArcGIS
WEEK 5 Discuss the use of photography and satellite date in GIS Outline raster data sources Load and geo-reference aerial photographs in ArcGIS Examine different display options when using raster images in ArcGIS
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Key textKey text Conolly J, Lake M 2006.Conolly J, Lake M 2006. Geographical Information Systems in Geographical Information Systems in
Archaeology: Cambridge Manuals in Archaeology. Archaeology: Cambridge Manuals in Archaeology. Cambridge Cambridge University Press. CambridgeUniversity Press. Cambridge
Geographical Information Systems are a powerful Geographical Information Systems are a powerful technology that offer a host of analytical possibilities technology that offer a host of analytical possibilities for investigating the spatial organisation of cultural for investigating the spatial organisation of cultural and human-environment relationshipsand human-environment relationships (p31) (p31)
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Data modelsData models
Data models and data structures: Data models and data structures: [are] the digital representation of [are] the digital representation of spatial phenomenaspatial phenomena
A GIS works by manipulating the A GIS works by manipulating the digital representations of real world digital representations of real world entities…[this is known as a] entities…[this is known as a]
data modeldata model
(Conolly and Lake, 2006: 24)(Conolly and Lake, 2006: 24)
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Two main types of Data models in GIS
Vector– Objects represented as nodes (X,Y points)
and connecting lines, attributes of objects attached as database tables
Raster– Geographical space represented as a grid of
cells, numerical values represent attributes of each cell
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Vector and Raster GISVector and Raster GIS
Forest Lake Grassland
Vector Raster
RoadSite
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StrengthsStrengths
Vector Spatial precision Compact data storage Scalable presentation Object based Database linkage
Raster Analytical capabilities Surfaces Continuous quantities Pixellated data Photographs
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Vector applicationsVector applications
Spatially referenced database applications (information about objects):• Location maps• Sites and Monuments• Artefacts
Mapping applications Triangulated Irregular Network (TIN)
elevation models
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Vector applicationsVector applications
Downside:• Very CPU intensive• Boundedness• Elevation is hard to express without a
TIN
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Raster applicationsRaster applications
Each cell can be given:Each cell can be given:• A quantitative value that signals the mean A quantitative value that signals the mean
elevationelevation• a single attributea single attribute
This is simple, in comparison to a vector, This is simple, in comparison to a vector, but that is it’s strength:but that is it’s strength:• It can be mathematically manipulated and It can be mathematically manipulated and
displayed much quicker than a vectordisplayed much quicker than a vector Fuzzy boundariesFuzzy boundaries Map algebraMap algebra
(Conolly and Lake, 2006: 28)(Conolly and Lake, 2006: 28)
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Raster applicationsRaster applications
Downside:Downside:• Fixed resolution (not multiscalar)Fixed resolution (not multiscalar)• It’s difficulty in representing discrete It’s difficulty in representing discrete
entities (too blocky)entities (too blocky)• Limited ability to handle multiple Limited ability to handle multiple
attribute data through a DBMSattribute data through a DBMS
(Conolly and Lake, 2006: 30-1)(Conolly and Lake, 2006: 30-1)
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The good news: Hybridisation
Vector/raster systems Most modern GIS software packages combine both
vector and raster capabilities
Image processing Aerial and satellite integration
ESRI desktop GIS suite ArcView
ArcCatalog and ArcMap
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The good news: HybridisationThe good news: Hybridisation Vector/raster systems
Most modern GIS software packages combine both vector and raster capabilities
Image processing• Aerial and satellite integration• DBMS integration
ESRI desktop GIS suite (www.esri.com)• Arc Info • ArcEditor• ArcView
ArcCatalog and ArcMap• ArcReader• ArcGIS extensions
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Hybridisation through layers in Hybridisation through layers in ArcViewArcView
MSc lecture notes 2005/6
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Software CAD/CAM
• AutoCAD, Microstation Image processing
• MicroBrain, ERDAS Imagine Raster GIS
• Idrisi, Grass (Unix), Grassland, Spans, MapII (Mac)
Vector GIS• ArcInfo, ArcGIS, MGE
Desktop mapping• ArcView ≤3, MapInfo
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Map objects
Point
Line/Polyline
Area/Region/Polygon
Text ABC
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Database linkageMap objects = attributes
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Most mapping applications are intimately linked with a database of objects:
• Territories
• Historical records
• Sites
• Museum objects
• Features
• Excavated/collected artefacts
Mapping to Database
Attributes
Graphical objects
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Layers / themes
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Why themes? Logical breakdown of data - related
objects in each theme Assemble maps for different purposes
by combining themes Examine interaction between themes,
create new themesPaper maps use symbolism to distinguish between layers, to compensate for the limitations of the technology
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Data collection (1)
Conventional databases• Point data
• Attributes for line & area objects
Digital vector data sources• Geographically referenced
– Worldwide, DCW
– BGS
– National (e.g. Ordnance Survey)
– Other e.g. Developers plans etc
• Drafting / surveyors’ plans (DXF)
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Data collection (2)
Map digitising Considerations:
• Accuracy, costs, heads-up/down
• Projection, geodetic system, topology
• Topographic / projected
• Plans / unprojected
• Historical maps & plans
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Data collection (3) EDM, GPS & conventional survey
• Architectural survey Field survey & recording
• Sites• Survey units / material count• Individual artefact locations
Surface collection Excavation
– Units & features as objects– 3D / volumetric systems / voxels
• Vastly increased data requirements– Artefacts