SVY2001: Databases for GIS

Transcription

1 SVY2001: Databases for GIS Lecture 15: Introduction to GIS and Attribute Data Management. Dr Stuart Barr School of Civil Engineering & Geosciences University of Newcastle upon Tyne. Lecture 3: Relational database normalisation 1 Lecture Objectives & Contents Objectives: To Cover the traditional approach to modelling spatial and attribute data within Geographical Information Systems. Contents: GIS, data & analysis. Representing the spatial component. Attribute representation. Typical GIS operations and attribute implications. Lecture 3: Relational database normalisation 2 1

2 Geographical Data Burrough & McDonnell (1998)... all geographical phenomenon can, in 2 dimensions at least, be represented by three basic entity types : P(X,Y) P1(X,Y) P2(X,Y) P1(X,Y) P2(X,Y) P5(X,Y) P4(X,Y) P3(X,Y) Lecture 3: Relational database normalisation 3 Geographical Data Each type of geographical data has several components: A Location component - a description of where it is and its geometric/geographical extent. An attribute component - non-spatial information describing the geographical entity. Lecture 3: Relational database normalisation 4 2

3 Organising Space in the GIS The most popular approach is to divide space into thematic layers which form the fundamental basis of analysis. A further important concept of GIS layers is Tiling: Spatial composting of geographically coincident layers. Assists in storage and handling of very large data-sets. Lecture 3: Relational database normalisation 5 The Two Spatial Data Models Vector Raster Lecture 3: Relational database normalisation 6 3

4 Vector Data Structures Vector data structures fall in to one of two different types depending on whether they do or do not represent/encode The geometric relationships that exist between entities located in space. It can be thought of as the study of how entities are organised relative to one another - whether they are connected,, adjacent or contained. Topological relations are invariant to stretching, bending, rotation and scaling. Lecture 3: Relational database normalisation 7 Vector Topological Arc-Node Lecture 3: Relational database normalisation 8 4

5 Vector Topological Polygon-Arc Poly Arc 1 1, 3, 4 2 2, 3, 5 Arc Coordinates 1 (1,8), (1,3) 2 (1,3), (3,4) Lecture 3: Relational database normalisation 9 Vector Data Structures - Topological In many GIS packages vector topology has to be explicitly built (e.g., ArcGIS Build command). If it is not then we have a simple spaghetti structure. Below is an arc attribute table no topology is present, hence we do not know which Nodes form Arcs. Lecture 3: Relational database normalisation 10 5

6 Vector Data Structures - Topological The coverage after Arc topology has been built in ArcGIS. Look at what we now know about the geometric connectivity. Lecture 3: Relational database normalisation 11 Vector & Attribute Storage Traditionally vector topology and attribute information stored in separate files. E.g., ARC/INFO coverages (predecessor to ArcGIS): ARC vector topology. INFO partial relational data structure. ARC - Geometry INFO - Attribute Points PNT Lines AAT Polygons PAT Lecture 3: Relational database normalisation 12 6

7 Vector & Attribute Storage It is possible to view and manage geometry and attribute simultaneously BUT in most GIS stored separately. Lecture 3: Relational database normalisation 13 Vector & Attribute Operations - JOIN Join Label NEWPOP Lecture 3: Relational database normalisation 14 7

8 Vector & Attribute Operations: RELATE Relate Label POP Lecture 3: Relational database normalisation 15 The Overlay Operation - Union Lecture 3: Relational database normalisation 16 8

9 The Overlay Operation - Union Lecture 3: Relational database normalisation 17 The Overlay Operation & Attributes: Union The overlay operation changes not only the visible spatial pattern BUT also the attributes. They are joined and in some cases duplicated. Lecture 3: Relational database normalisation 18 9

10 The Overlay Operation - Intersection Lecture 3: Relational database normalisation 19 The Overlay Operation & Attributes: Intersection The overlay operation changes not only the visible spatial pattern BUT also the attributes. They are joined and in some cases duplicated. Lecture 3: Relational database normalisation 20 10

11 Attribute Operations - Selection Lecture 3: Relational database normalisation 21 Attribute Operations Selection by Location All Census output areas that fall completely within an urban area. Lecture 3: Relational database normalisation 22 11

12 A Once in a Lifetime Offer! If today s material is new consider checking out the online SVY20004 material and possibly doing a couple of the ArcGIS practicals. Url: Username: SVY2004_students Password: intersection Lecture 3: Relational database normalisation 23 Reading Lecture 15 Burrough & McDonnell - Principals of Geographical Information Systems. Pages Longley, P.A., Goodchild, M.J., Maguire, D.J., and Rhind, D.W., Geographic Information Systems and Science. Pages Worboys, M.F., and Duckham, M., GIS: A Computing Perspective. Pages & (Note: written very much from a computer science perspective). Franklin, W.M.R., Computer Systems and Low-Level Data Structures for GIS. In, Maguire, D.J., Goodchild, M.F., and Rhind, D.W., (eds), Geographical Information Systems: Principles and Applications. pp Egenhofer, M.J., and Herring, J.R., High-Level Spatial data Structures for GIS. In, Maguire, D.J., Goodchild, M.F., and Rhind, D.W., (eds), Geographical Information Systems: Principles and Applications. pp Piquet, D.J., A Conceptual Framework and Comparison of Spatial Data Models. Cartographica, 21(4), pp Healey, R.G., Database Management Systems. In, Maguire, D.J., Goodchild, M.F., and Rhind, D.W., (eds), Geographical Information Systems: Principles and Applications. pp Jacobson, C.R., Non-spatial Database Models, NCGIA Lecture 3: Relational database normalisation 24 12

13 SVY2001 L15: Introduction to GIS & Attribute Data Management Today we have: Reviewed the main spatial data structures used in GIS. Considered how attribute data is managed. Looked at the most common GIS operations. Next lecture: From Geo-relational lto Arc SDE. Lecture 3: Relational database normalisation 25 13