Geospatial Tools and Techniques€¦ · Spatial and Attribute Data that Leads to Information •...
Transcript of Geospatial Tools and Techniques€¦ · Spatial and Attribute Data that Leads to Information •...
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Geospatial Tools and
Techniques
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Azimuth (degrees east of north)
and Airport use:
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Vocabulary Activity
• Polygon •••• Altitude
• Line •••• Topography
• Prime Meridian •••• Demographic
• Latitude •••• Economics
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Vocabulary Activity
• Spatial •••• Longitude
• Analysis •••• Equator
• Point •••• Azimuth
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What is GIS?
• Geographic Information Systems
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GIS--What is it?No easy answer anymore!
• Geographic/Geospatial Information
– information about places on the earth’s surface
– knowledge about “what is where when”
(Don’t forget time!)
– Geographic/geospatial: synonymous
• GIS--what’s in the S?
– Systems: the technology
– Science: the concepts and theory
– Studies: the societal context
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Geographic Information Technologies• Global Positioning Systems (GPS)
– a system of earth-orbiting satellites which can provide precise (100 meter to sub-cm.) location on the earth’s surface (in lat/long coordinates or equiv.)
• Remote Sensing (RS)
– use of satellites or aircraft to capture information about the earth’s surface
– Digital ortho images a key product (map accurate digital photos)
• Geographic Information Systems (GIS)
– Software systems with capability for input, storage, manipulation/analysis and output/display of geographic (spatial) information
GPS and RS are sources of input data for a GIS.
A GIS provides for storing and manipulating GPS and RS data.
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Decision
GIS ProcessOutput
GIS
analysis
Import or
build datasets
Define GIS
criteria
Define
problemDecision
GIS ProcessOutput
GIS
analysis
Import or
build datasets
Define GIS
criteria
Define
problem
Geographic Information
Systems
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Simply said:
Geographic » maps
Information » data
System » digital
A GIS links information to geographic location
(connects the what to the where), allowing you to
seek patterns and relationships that may not
otherwise be apparent.
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So, each layer contains 2 kinds of data that
leads to information:
• Spatial data -> information –location and shape of the geographic features
• Attribute data -> information –other characteristics of the features
A layer serves as a shortcut to the data. It also tells ArcMap how the data should be drawn.
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Spatial and Attribute Data that
Leads to Information• Spatial data (where)
– specifies location
– stored in a shape file, geodatabase or similar geographic file
• Attribute (descriptive) data (what, how much, when)
– specifies characteristics at that location, natural or human-created
– stored in a data base table
GIS systems traditionally maintain spatial and attribute data separately, then “join” them for display or analysis
– for example, in ArcMap, the Attributes of … table is used to link a shapefile (spatial structure) with a data base tablecontaining attribute information in order to display the attribute data spatially on a map
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THREE SPATIAL
COMPONENTS
• Point
• Line
• Polygon
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Two Basic GIS Data Models
• Vector GIS
– Represent space with points, lines, and polygons
– One spatial feature, many attributes
– Does not fill space
– Relatively intuitive visualization – maps
• Raster GIS
– Represents space with uniform cells on a grid
– One cell, one attribute
– Fills space
– Visualization not as intuitive – can look very odd
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Representing Data with Raster and Vector Models
Raster Model
• area is covered by grid with (usually) equal-sized, square cells
• attributes are recorded by assigning each cell a single value based on the majority feature (attribute) in the cell, such as land use type.
• Image data is a special case of raster data in which the “attribute” is a reflectance value from the geomagnetic spectrum
– cells in image data often called pixels (picture elements)
• Vector Model
The fundamental concept of vector GIS is that all geographic features in the real work can be represented either as:
• points or dots (nodes): trees, poles, fire plugs, airports, cities
• lines (arcs): streams, streets, sewers,
• areas (polygons): land parcels, cities, counties, forest, rock type
Because representation depends on shape, ArcView refers to files containing vector data as shapefiles
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0 1 2 3 4 5 6 7 8 9
0 R T
1 R T
2 H R
3 R
4 R R
5 R
6 R T T H
7 R T T
8 R
9 R
Real World
Vector RepresentationRaster Representation
Concept of
Vector and Raster
line
polygon
point
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Representing Spatial Elements
• RASTER
• VECTOR
• Real World
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Vector or Raster?
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Vector or Raster?