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United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis

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Spatial Analysis & Dissemination of Census Data United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis Nairobi, Kenya, 14-17 September, 2010 – PowerPoint PPT presentation

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Title: United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis


1
Spatial Analysis Dissemination of Census Data
2
Outline
  • Geographic Database
  • Spatial Analysis Techniques
  • Examples

3
Geographic Database
  • Geographical features (Conceptual Model)
  • Components selection
  • Attributes
  • Structure
  • Spatial Relationships (explicit -Topolgy)

4
Spatial relationships
  • Logical connections between spatial objects
    represented by points, lines and polygons
  • e.g.,
  • - point-in-polygon
  • - line-line
  • - polygon-polygon

5
Spatial Operations
  • adjacent to
  • connected to
  • near to
  • intersects with
  • within
  • overlaps
  • etc.

6
Spatial Analysis Techniques
  • the main use of spatial analysis is for census
    products and services
  • Techniques include queries, distance
    measurements, buffering, linear interpolation,
    point pattern analysis, and cartograms, etc.
  • All offer functionality beyond standard thematic
    (choropleth) mapping, with many tools now
    available in both commercial and open-source
    software programs.

7
Spatial Analysis Query
  • select features by their attributes
  • find all districts with literacy rates lt 60
  • select features by geographic relationships
  • find all family planning clinics within this
    district
  • combined attributes/geographic queries
  • find all villages within 10km of a health
    facility that have high child mortality
  • Query operations are based on the SQL
    (Structured Query Language) concept

8
Examples
What is at?
Features that meet a set of criteria
9
is nearest to
  • Point/point
  • Which family planning clinic is closest to the
    village?
  • Point/line
  • Which road is nearest to the village
  • Same with other combinations of spatial features

10
is near to Buffer Operations
  • Point buffer
  • Affected area around a Hospital
  • Catchment area of a water source

11
is near to Buffer Operations
  • Point buffer
  • Affected area around a polluting facility
  • Catchment area of a water source

12
Buffer Operations
  • Line buffer
  • How many people live near the polluted river?
  • What is the area impacted by highway noise?

13
Buffer Operations
  • Polygon buffer
  • Area around a reservoir where development should
    not be permitted

14
Spatial Analysis Techniques
  • point-in-polygon analysis
  • Determines whether a point lies inside or outside
    a polygon.
  • Can be used to compare geo-coded village
    centroids lying inside and outside hazardous
    areas such as tropical storm tracks or earthquake
    zones.
  • Polygon overlay analysis
  • Involves comparison between the locations of two
    different polygonal data layers.
  • For example, the boundaries of two administrative
    districts could be compared to troubleshoot
    errors in the field enumeration process

15
is within point in polygon
  • Which of the cholera cases are within the
    containment area

16
  • Problem
  • We may have a set of point coordinates
    representing clusters from a demographic survey
    and we would like to combine the survey
    information with data from the census that is
    available by enumeration areas.

Solution Point-in-Polygon operation will
identify for each point the EA area into
which it falls and will attach the census data to
the attribute record of that survey point.
17
Spatial aggregation
  • Example of Spatial aggregation
  • fusion of many provinces constituting an economic
    region

18
Spatial data transformation interpolation
Example 1 Based on a set of station
precipitation surface estimates, we can create a
raster surface that shows rainfall in the entire
region
13.5
20.1





26.0
27.2
12.7
15.9
24.5
26.1
19
Example of linear interpolation creating contours
20
Thiessen polygons illustrated
Spatial Analysis Techniques
  • Thiessen polygons
  • Have the unique property that each polygon
    contains only one input point (e.g. settlements),
    and any location within a polygon is closer to
    its associated point than to the point of any
    other polygon.
  • This method assumes that the values of the
    unsampled data are equivalent to those of the
    sampled points.

21
Areas of influence
  • Commuting distances daily commuters flow

22
Modeling/Geoprocessing
  • modeling identify or predict a process that has
    created or will create a certain spatial pattern
  • diffusion how is the epidemic spreading in the
    province?
  • interaction where do people migrate to?
  • what-if scenarios if the dam is built, how many
    people will be displaced?

23
Modelling smoothing
  • Evolution of the population beetwen two censuses

24
Spatial Analysis Techniques
  • Cartograms
  • sometimes used to display census results
  • The areas of the original polygons are expanded
    or contracted based on their attribute values
    such as population size or voting habits

25
Location-allocation problems
  • Site selection
  • Optimal allocation
  • Multicriteria Analysis

26
THANK YOU!
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