2. COMPUTERS AND STATISTICS IN ARCHAEOLOGY Week 4. Geographic Information Systems (GIS) - 2 © Richard Haddlesey www.medievalarchitecture.net

3. Aims l WEEK 4 l Examine the differences between vector and raster graphics l Discuss which data types are best represented by each l Examine how ArcGIS treats vector graphics l Outline vector data sources l Create new vector themes by digitising in ArcGIS l WEEK 5 l Discuss the use of photography and satellite date in GIS l Outline raster data sources l Load and geo-reference aerial photographs in ArcGIS l Examine different display options when using raster images in ArcGIS

4. Key text Conolly J, Lake M 2006. Geographical Information Systems in Archaeology: Cambridge Manuals in Archaeology. Cambridge University Press. Cambridge Conolly J, Lake M 2006. Geographical Information Systems in Archaeology: Cambridge Manuals in Archaeology. Cambridge University Press. Cambridge Geographical Information Systems are a powerful technology that offer a host of analytical possibilities for investigating the spatial organisation of cultural and human- environment relationships (p31) Geographical Information Systems are a powerful technology that offer a host of analytical possibilities for investigating the spatial organisation of cultural and human- environment relationships (p31)

5. Data models Data models and data structures: [are] the digital representation of spatial phenomena Data models and data structures: [are] the digital representation of spatial phenomena A GIS works by manipulating the digital representations of real world entities…[this is known as a] data model A GIS works by manipulating the digital representations of real world entities…[this is known as a] data model (Conolly and Lake, 2006: 24)

6. Two main types of Data models in GIS l Vector –Objects represented as nodes (X,Y points) and connecting lines, attributes of objects attached as database tables l Raster –Geographical space represented as a grid of cells, numerical values represent attributes of each cell

7. Vector and Raster GIS Forest Lake Grassland Vector Raster Road Site

8. Strengths Vector l Spatial precision l Compact data storage l Scalable presentation l Object based l Database linkage Raster l Analytical capabilities l Surfaces l Continuous quantities l Pixellated data l Photographs

9. Vector applications Spatially referenced database applications (information about objects): Location maps Sites and Monuments Artefacts Mapping applications Triangulated Irregular Network (TIN) elevation models

10. Vector applications Downside: Very CPU intensive Boundedness Elevation is hard to express without a TIN

11. Raster applications Each cell can be given: Each cell can be given: A quantitative value that signals the mean elevationA quantitative value that signals the mean elevation a single attributea single attribute This is simple, in comparison to a vector, but that is its strength: This is simple, in comparison to a vector, but that is its strength: It can be mathematically manipulated and displayed much quicker than a vectorIt can be mathematically manipulated and displayed much quicker than a vector Fuzzy boundaries Fuzzy boundaries Map algebra Map algebra (Conolly and Lake, 2006: 28)

12. Raster applications Downside: Downside: Fixed resolution (not multiscalar)Fixed resolution (not multiscalar) Its difficulty in representing discrete entities (too blocky)Its difficulty in representing discrete entities (too blocky) Limited ability to handle multiple attribute data through a DBMSLimited ability to handle multiple attribute data through a DBMS (Conolly and Lake, 2006: 30-1)

13. The good news: Hybridisation Vector/raster systems l Most modern GIS software packages combine both vector and raster capabilities l Image processing l Aerial and satellite integration l ESRI desktop GIS suite l ArcView l ArcCatalog and ArcMap

14. The 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

15. Hybridisation through layers in ArcView MSc lecture notes 2005/6

16. Software l CAD/CAM AutoCAD, Microstation l Image processing MicroBrain, ERDAS Imagine l Raster GIS Idrisi, Grass (Unix), Grassland, Spans, MapII (Mac) l Vector GIS ArcInfo, ArcGIS, MGE l Desktop mapping ArcView 3, MapInfo

17. Map objects l Point l Line/Polyline l Area/Region/Polygon l Text ABC

18. Database linkage Map objects = attributes

19. l 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

20. Layers / themes

21. Why themes? l Logical breakdown of data - related objects in each theme l Assemble maps for different purposes by combining themes l Examine interaction between themes, create new themes Paper maps use symbolism to distinguish between layers, to compensate for the limitations of the technology

22. Data collection (1) l Conventional databases Point data Attributes for line & area objects l Digital vector data sources Geographically referenced –Worldwide, DCW –BGS –National (e.g. Ordnance Survey) –Other e.g. Developers plans etc Drafting / surveyors plans (DXF)

23. Data collection (2) l Map digitising l Considerations: Accuracy, costs, heads-up/down Projection, geodetic system, topology Topographic / projected Plans / unprojected Historical maps & plans

24. Data collection (3) l EDM, GPS & conventional survey Architectural survey l Field survey & recording Sites Survey units / material count Individual artefact locations l Surface collection l Excavation –Units & features as objects –3D / volumetric systems / voxels Vastly increased data requirements –Artefacts