Geographic Information Systems for Public Policy - Lecture V

Raster Data Models

Sergio Rey

Last Time

  • Vector Attributes
  • Table Joins
  • Virtual Layers

Today

  • Raster Data Model
  • Conversions
  • Rasters in Public Policy/Social Sciences

Raster Data Model

  • Rasters composed of a matrix of pixels (cells)
  • Each pixel contains a value representing the conditions for the area covered by that pixel
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Advantages of Rasters

  • Representing continuous spatial variation
  • More efficient than small polygons (in the vector model)
    figure

Georeferencing Rasters

  • Defines the correspondence between each pixel and location on the earth’s surface
  • Coordinates of top left pixel in the images
  • Size of each pixel in X and Y direction
  • Rotation angle

Raster in QGIS

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Raster in QGIS

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Sources of raster data

Remote Sensing Satellites

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Remote Sensors

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Planet

213_planet

Earth Engine Timelapse

‘url’

Remote Sensing Imagery Resolution

  • Spatial Resolution
  • Spectral Resolution
  • Temporal Resultion

Spatial Resolution

How much area is represented in each pixel

  • MODIS 500m x 500m
  • SPOT5 satellites: 10m x 10m
  • Areal Photography, drones: 50cm x 50cm

Remember: images with pixel size covering a small area are called high resolution images.

Spatial Resolution and Scale

Spectral Resolution

  • The number of spectral bands in which a sensor can collect reflected radiance
  • Choice depends upon application of use
  • Different types of ground targets have different spectral signatures
213_planet

Temporal Resolution

Revisit Periods for Satellites

  • SPOT5 - 3 days
  • Modis - daily
  • Airborne - as needed

Conversions

Which Model?

vector v. raster

Vector to raster conversion

240_vec2ras

Raster to vector conversion

241_ras2vec

Rasters in GIS for Public Policy

  • Measures of environmental variables
  • Risk surfaces
  • Dasymetric mapping and areal interpolation

Environmental variables

Freeman et al. (2017) “Willingness to pay for clean air in China”

303_willingness

FEMA: Risk Surface

307_risk

Dasymetric Mapping

301_dasymetric

NSF-Neighborhoods

309_nsf_neighborhoods

Interpolation and Harmonization

Tobler

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Tobler: Voting Precincts

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Tobler: Dasymetric

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National Land Cover Database

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Next Up

  • Coordinate Reference Systems

Creative Commons License
GIS for Public Policy’20 by Sergio Rey is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.