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This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Recap Mapping and Error Law and IPR Metadata.

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Presentation on theme: "This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Recap Mapping and Error Law and IPR Metadata."— Presentation transcript:

1 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Recap Mapping and Error Law and IPR Metadata Finding Data Data Principles of GIS

2 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Recap Attributes, footprints and topologies

3 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping precision and accuracy Precision implies the degree to which a measurement is refined Accuracy that the measurement taken is correct within the precision indicated

4 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping precision and accuracy Precise and accurate Precise but inaccurate imprecise and inaccurate imprecise but accurate

5 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping scale Precision and accuracy are functions of how data are produced or gathered The perfect map is not 100% accurate or precise. It is FIT FOR PURPOSE

6 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping precision and accuracy precise and accurate precise but inaccurate imprecise but accurate imprecise and inaccurate

7 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping representing the world The map is only a representation of the world. There are 3 main transformations that are required to transform the world into a map: projection generalization referencing

8 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: projection There are a variety of different projections used to turn the 3-dimensional world into 2 dimensions

9 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: projection Flat Earth models are appropriate for local survey mapping up to about 10km in range Spheroid transformations are appropriate for navigation across longer distances Ellipsoid transformations are necessary for large scale mapping (or mapping that uses GPS) BUT The earth is irregular so there are different reference ellipsoids, spheroids and datums used for this transformation

10 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: projection Azimuthal projectionCylindrical projection Conic projection Different projections have their own characteristics and uses. They all distort the properties of the Earth, but do so differently.

11 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: error There are six main types of distortion in mapping: shape distance area direction scale angle

12 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: error Different types of mapping handle map distortion differently conformal maps can be used to describe shape well, but not area equal distance maps compromise everything but distances azimuthal maps protect angles

13 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: error distortion is not constant Azimuthal projections distort from the centre Cylindrical projections distort from the equator Scale is only exact on OS mapping at 2 central axes 180km either side of the central meridian 180 KM W 180 Km E Error at central meridien = !: Error = 1:1 Error increases as a function of distance from the equator

14 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: error The point is that the geo-spatial footprint necessarily contains error. It can’t be avoided, but can be managed. This impacts on any questions we ask of our GIS and the nature of the answers that we get back.

15 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Understanding mapping: generalisation For mapping to be useful certain known elements of the world are discarded. The greater the scale, the more is discarded. Shape, direction and connection may be lost.

16 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002)

17 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Error is inevitable! It can be managed but not eradicated: it is easy to increase error, harder to reduce it 1:1250 “flat earth” survey Casini Projection 1:50,000 OS WGS datum Ellipsoid transformation Aerial photo

18 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Fundamentals of copyright Mapping is very expensive to produce Copyright is protected very aggressively for GI data Aspects of transformation may also be copyright Failure to comply may end in severe sanction Limited prescribed exemptions for education Raster is less restricted than vector Compiled images less restricted than uncompiled Desktop work is less restricted than networked Don’t just digitise your favourite map! Protect your own copyright! Principles of GIS: Intellectual Property Rights

19 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Freedom of Information Environmentally sensitive places EIR Data Protection Laws Liability Database Right Principles of GIS: Intellectual Property Rights

20 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Resource discovery metadata (DC / NGDF) Tracking changes Tracking IPR Documentation Guides to Good Practice Principles of GIS: the importance of metadata

21 This power point presentation and its contents are copyright of the Archaeology Data Service and WGK (2002) Finding Data: see your handouts


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