Title: Geographic Information Systems: an introduction Week III Data models contd The Nature of Geographic
1Geographic Information Systemsan
introductionWeek IIIData models contdThe
Nature of Geographic Data
2Last week
- Representing geographic data
- E.g. continuous fields, discrete objects
- Data models
- E.g. Raster, vector
3Data Model Levels
Reality
Human-oriented
Conceptual Model
Increasing Abstraction
Logical Model
Computer-oriented
Physical Model
4Logical Data Models Applications
- CAD
- Graphical
- Image
- Raster
- TIN
- Geo-relational
- Object
- Engineering design
- Simple mapping
- Image processing and analysis
- Spatial analysis / modeling
- Surface /terrain analysis / modeling
- Geoprocessing geometric features
- Features with behavior
5Raster and Vector Models
- Raster implementation of field conceptual model
- Array of cells used to represent objects
- Useful as background maps and for spatial
analysis - Vector implementation of discrete object
conceptual model - Point, line and polygon representations
- Widely used in cartography, and network analysis
6Rasters and Vectors
- How to represent phenomena conceived as fields or
discrete objects? - Raster
- Divide the world into square cells
- Register the corners to the Earth
- Represent discrete objects as collections of one
or more cells - Represent fields by assigning attribute values to
cells - More commonly used to represent fields than
discrete objects
7Legend
Mixed conifer
Douglas fir
Oak savannah
Grassland
Raster representation. Each color represents a
different value of a nominal-scale field denoting
land cover class.
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9Characteristics of Rasters
- Pixel size
- The size of the cell or picture element, defining
the level of spatial detail - All variation within pixels is lost
- Assignment scheme
- The value of a cell may be an average over the
cell, or a total within the cell, or the
commonest value in the cell - It may also be the value found at the cells
central point
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13Vector Data
- Used to represent points, lines, and areas
- All are represented using coordinates
- One per point
- Areas as polygons
- Straight lines between points, connecting back to
the start - Point locations recorded as coordinates
- Lines as polylines
- Straight lines between points
14Vector Data
.ancaster
POINTS
POINTS
POLYGON
POLYGON
LINES
LINES
Millbrook Lane
ANNOTATION
ANNOTATION
NODES
NODES
15Vector - Land Records
Surveyed feature
20.37
26.23
R 10
45.81
45.81
13
12
35.44
30.5
26.23
GIS
Survey
Link
/
/
/
Survey point
/
9
/
/
Computation
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17Raster vs Vector
- Volume of data
- Raster becomes more voluminous as cell size
decreases - Raster is vaster
- Source of data
- Remote sensing, elevation data come in raster
form - Vector favored for administrative data
- Vector is more appropriate when storing large
amounts of attribute information. - Software
- Some GIS better suited to raster, some to vector
18Data Model Levels
Reality
Human-oriented
Conceptual Model
Increasing Abstraction
Logical Model
Computer-oriented
Physical Model
19Data Models and Spatial Analysis
- Raster v. vector?
- Picture of a large burn
- Picture of an urban landscape
- Picture of burning houses
- Map of burning houses
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26Geo-relational Model
27Formats of feature data models in ArcGIS
- Georelational models
- Coverages
- Shapefiles
- Database Management System (DBMS)
- Geodatabase
28Coverages
- Traditional model
- for complex
- (multiple feature types) geoprocessing
environments
29Coverages
.
- primary
- composite
- secondary
routes sections regions annotation ticks links
30Shapefiles
- Simple, open,
- flatfile based
- format for single
- data features
31Geodatabase
- Object-based
- data model
- where all features
- are contained
- in database
- features can
- exhibit behavior
32Compression techniques
No compression
Run length encoding (lossless)
33 ADRG - National Imagery and Mapping Agency
(NIMA)'s ARC Digitized Raster Graphics BIL -
Band Interleaved by Line (image format linked
with satellite derived imagery) CADRG - National
Imagery and Mapping Agency (NIMA)'s Compressed
ARC Digitised Raster Graphics (nominal
compression of 551 over ADRG) CIB - National
Imagery and Mapping Agency (NIMA)'s Controlled
Image Base (type of Raster Product Format)
Digital raster graphic (DRG) - digital scan of a
paper USGS topographic map ECW - Enhanced
Compressed Wavelet (from ERMapper). A compressed
wavelet format, often lossy. ESRI grid - binary
and ASCII raster formats used by ESRI GeoTIFF -
TIFF variant enriched with GIS relevant metadata
IMG - ERDAS IMAGINE image file format MrSID -
Multi-Resolution Seamless Image Database (by
Lizardtech). A compressed wavelet format, often
lossy.
34Vector formats Geography Markup Language (GML) -
XML based open standard (by OpenGIS) for GIS data
exchange DXF - Contour elevation plots in
AutoCAD DXF format Shapefile - ESRI's open,
hybrid vector data format using SHP, SHX and DBF
files Simple Features - Open Geospatial
Consortium specification for vector data MapInfo
TAB format - MapInfo's vector data format using
TAB, DAT, ID and MAP files National Transfer
Format (NTF) - National Transfer Format (mostly
used by the UK Ordnance Survey) TIGER -
Topologically Integrated Geographic Encoding and
Referencing Vector Product Format - National
Imagery and Mapping Agency (NIMA)'s format of
vectored data for large geographic databases.
GeoMedia - Intergraph's Microsoft Access based
format for spatial vector storage. ISFC -
Intergraph's Microstation based CAD solution
attaching vector elements to a relational
Microsoft Access database Personal Geodatabase -
ESRI's closed, integrated vector data storage
strategy using Microsoft's Access MDB format
Coverage - ESRI's closed, hybrid vector data
storage strategy. Legacy ArcGIS Workstation /
ArcInfo format with reduced support in ArcGIS
Desktop lineup
35Grid formats (for elevation) USGS DEM - The USGS'
Digital Elevation Model DTED - National Imagery
and Mapping Agency (NIMA)'s Digital Terrain
Elevation Data GTOPO30 - Large complete Earth
elevation model at 30 arc seconds SDTS - The
USGS' successor to DEM Other formats Binary
Terrain - The Virtual Terrain Project's Binary
Terrain format Well-known text (WKT) ASCII
spatial projection description (ESRI uses a .prj
extension) Well-known binary (WKB) - Binary
spatial projection description
36Geo-relational Model
37Formats of feature data models in ArcGIS
- Georelational models
- Coverages
- Shapefiles
- Object model
- Geodatabase
38Coverages
Traditional model for complex geoprocessing
environments
- Topologically correct
- Data processing and spatial analysis
- Complex data structure
- Difficult interchange (E00)
- Multiple feature types
.
- primary
- composite
- secondary
routes sections regions annotation ticks links
39Coverages
40Shapefiles
- Simple, open, flatfile based format for single
data features
- Single feature type within one file
- No topology
- Easy to transport
- Open
41Shapefiles
42Geodatabase
- Object-based data model where all features are
contained in database features can exhibit
behavior
- Multiple features stored as tables
- Data processing topology
- Object oriented instead of restricted to points,
lines, polys - Resides in traditional database
43Geodatabase
44Topology
- Field within mathematics.
- The study of the general abstract nature of
continuity or "closeness" on spaces. - System administrators actually describe computer
networks as being topologic - Bus topology
- Ring topology
- Star topology
- Leonhard Euler
- The solution of a problem relating to the
geometry of position 1736. - Euler was aware that he was dealing with a
different type of geometry where distance was not
relevant.
45Consider the problem of building a fusion reactor
which confines a plasma by a magnetic field.
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47The solution of a problem relating to the
geometry of position
48Topology
- Science and mathematics of geometric
relationships - Simple features topological rules
- Connectivity
- Adjacency
- Shared nodes / edges
- Topology uses
- Data validation
- Spatial analysis (e.g. network tracing, polygon
adjacency)
49Topology and GIS
- Topology in GIS is generally defined as the
spatial relationships between adjacent or
neighboring features. - Two types of topology
- Polygon topology
- Line topology
- three advantages of incorporating topology in GIS
databasesdata management, data correction and
spatial analysis
50Data correction and storage
51Topology and spatial analysis
- Adjacency
- Connectivity (network models)
- Containment
52Polygon Topology Model
53Polygon Topology Contiguity
54Definitions
- A method of analysis is spatial if the results
depend on the locations of the objects being
analyzed - move the objects and the results change
- results are not invariant under relocation
- Spatial analysis requires both attributes and
locations of objects - a GIS has been designed to store both
55Spatial Autocorrelation
- Spatial autocorrelation is determined both by
similarities in position, and by similarities in
attributes - Sampling interval
- Self-similarity
Tobler
56Spatial autocorrelation measures
n number of objects in the sample i,j any two of
the objects z the value of the attribute
of interest for object i c the similarity
of is and js attributes w the similarity
of is and js locations
i
i,j
i,j