Geographic Information Systems: an introduction Week III Data models contd The Nature of Geographic - PowerPoint PPT Presentation

1 / 56
About This Presentation
Title:

Geographic Information Systems: an introduction Week III Data models contd The Nature of Geographic

Description:

GeoMedia - Intergraph's Microsoft Access based format for spatial vector storage. ... based CAD solution attaching vector elements to a relational Microsoft ... – PowerPoint PPT presentation

Number of Views:236
Avg rating:3.0/5.0
Slides: 57
Provided by: drc46
Category:

less

Transcript and Presenter's Notes

Title: Geographic Information Systems: an introduction Week III Data models contd The Nature of Geographic


1
Geographic Information Systemsan
introductionWeek IIIData models contdThe
Nature of Geographic Data

2
Last week
  • Representing geographic data
  • E.g. continuous fields, discrete objects
  • Data models
  • E.g. Raster, vector

3
Data Model Levels
Reality
Human-oriented
Conceptual Model
Increasing Abstraction
Logical Model
Computer-oriented
Physical Model
4
Logical 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

5
Raster 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

6
Rasters 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

7
Legend
Mixed conifer
Douglas fir
Oak savannah
Grassland
Raster representation. Each color represents a
different value of a nominal-scale field denoting
land cover class.
8
(No Transcript)
9
Characteristics 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

10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
Vector 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

14
Vector Data
.ancaster
POINTS
POINTS
POLYGON
POLYGON
LINES
LINES
Millbrook Lane
ANNOTATION
ANNOTATION
NODES
NODES
15
Vector - 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
16
(No Transcript)
17
Raster 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

18
Data Model Levels
Reality
Human-oriented
Conceptual Model
Increasing Abstraction
Logical Model
Computer-oriented
Physical Model
19
Data 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

20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
Geo-relational Model
27
Formats of feature data models in ArcGIS
  • Georelational models
  • Coverages
  • Shapefiles
  • Database Management System (DBMS)
  • Geodatabase

28
Coverages
  • Traditional model
  • for complex
  • (multiple feature types) geoprocessing
    environments

29
Coverages
.
  • primary
  • composite
  • secondary

routes sections regions annotation ticks links
30
Shapefiles
  • Simple, open,
  • flatfile based
  • format for single
  • data features

31
Geodatabase
  • Object-based
  • data model
  • where all features
  • are contained
  • in database
  • features can
  • exhibit behavior

32
Compression 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.
34
Vector 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
35
Grid 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
36
Geo-relational Model
37
Formats of feature data models in ArcGIS
  • Georelational models
  • Coverages
  • Shapefiles
  • Object model
  • Geodatabase

38
Coverages
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
39
Coverages
40
Shapefiles
  • Simple, open, flatfile based format for single
    data features
  • Single feature type within one file
  • No topology
  • Easy to transport
  • Open

41
Shapefiles
42
Geodatabase
  • 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

43
Geodatabase
44
Topology
  • 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.

45
Consider the problem of building a fusion reactor
which confines a plasma by a magnetic field.
46
(No Transcript)
47
The solution of a problem relating to the
geometry of position
48
Topology
  • 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)

49
Topology 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

50
Data correction and storage
51
Topology and spatial analysis
  • Adjacency
  • Connectivity (network models)
  • Containment

52
Polygon Topology Model
53
Polygon Topology Contiguity
54
Definitions
  • 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

55
Spatial Autocorrelation
  • Spatial autocorrelation is determined both by
    similarities in position, and by similarities in
    attributes
  • Sampling interval
  • Self-similarity

Tobler
56
Spatial 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
Write a Comment
User Comments (0)
About PowerShow.com