1. Spatial Analysis & Dissemination of Census Data
An understanding of the spatial distribution of human activity provides valuable information on the analysis of settlement and neighborhood patterns and the distribution of residential, commercial, and industrial activities. It has been argued that social and spatial structure “feed upon one another” to, in a literal sense, eventually become each other. Knowing where the young and old live, tells us about the changing social relationships and their individual geographies. It is a basis for a better knowing of why society is organized as it is, making us to learn from history so that we properly plan. Dorling (1994) argues that spatial patterns of a population reflect the social structure. These patterns reflect a reality that impinges upon everyday lives; lives whose course is governed by that social structure, a social structure that is changing spatially.
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

2. Nairobi, Kenya, 14-17 September, 2010
Outline
Geographic Database
Spatial Analysis Techniques
Examples
“Spatial analysis can offer the census new ways to investigate data. Sometimes the only connection between two phenomena is their location in space. GIS can be a tool for data mining and even creating new, unique information. Spatial methods like buffering, finding distance between items, phenomena that expand in space and density of characters in a spatial unit. These types of queries are the essence of GIS. First use of these methods was done in investigating the 1995 census data. The 2006 census can help to establish a new framework, making GIS methods a real, independent research tools for use in the publication of the national statistics” (Israel report).
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

3. Nairobi, Kenya, 14-17 September, 2010
Geographic Database
Geographical features (Conceptual Model)
Components selection
Attributes
Structure
Spatial Relationships (explicit -Topolgy)
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

4. Spatial relationships
Logical connections between spatial objects represented by points, lines and polygons
e.g.,
- point-in-polygon
- line-line
- polygon-polygon
Fundamental Questions addressed by GIS
What is in a particular place?
Find the position of some object
What is the area of, the distance from specific object?
Find patterns- by looking at the distribution of features on the map instead of just an individual feature
Combination of data layers
Point in polygon operation
Line in polygon operation
Polygon overlay
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010 4

5. Nairobi, Kenya, 14-17 September, 2010
Spatial Operations
“adjacent to”
“connected to”
“near to”
“intersects with”
“within”
“overlaps”
etc.
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

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.
Although spatial analysis is sometimes used during the enumeration phase (clustering, for example, can aid in identifying housing units to be canvassed), the main use of spatial analysis is for census products and services.
A variety of techniques including buffering, linear interpolation, point pattern analysis, and cartograms, offer functionality beyond standard thematic (choropleth) mapping, with many tools now available in both commercial and open-source software programs.
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

7. Spatial Analysis: Query
select features by their attributes:
“find all districts with literacy rates < 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
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

8. Nairobi, Kenya, 14-17 September, 2010
Examples:
What is at…?
Features that meet a set of criteria
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

9. Nairobi, Kenya, 14-17 September, 2010
“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
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

10. “is near to”: Buffer Operations
Point buffer
Affected area around a Hospital
Catchment area of a water source
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

11. “is near to”: Buffer Operations
Point buffer
Affected area around a polluting facility
Catchment area of a water source
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

12. Nairobi, Kenya, 14-17 September, 2010
Buffer Operations
Line buffer
How many people live near the polluted river?
What is the area impacted by highway noise?
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

13. Nairobi, Kenya, 14-17 September, 2010
Buffer Operations
Polygon buffer
Area around a reservoir where development should not be permitted
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

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
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

15. “ is within”: point in polygon
Which of the cholera cases are within the containment area
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

16. Nairobi, Kenya, 14-17 September, 2010
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.
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

17. Nairobi, Kenya, 14-17 September, 2010
Spatial aggregation
Example of Spatial aggregation:
fusion of many provinces constituting an economic region
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

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
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

19. Nairobi, Kenya, 14-17 September, 2010
Example of linear interpolation creating contours
Illustration showing how contour lines of elevation can be derived through linear interpolation from a satellite image.
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

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.
Thiessen polygons illustrated
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

21. Nairobi, Kenya, 14-17 September, 2010
Areas of influence
Commuting distances: daily commuters flow
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

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?
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

23. Nairobi, Kenya, 14-17 September, 2010
Modelling: smoothing
Evolution of the population beetwen two censuses
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

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
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

25. Location-allocation problems
Site selection
Optimal allocation
Multicriteria Analysis
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010

26. Nairobi, Kenya, 14-17 September, 2010
THANK YOU!
United Nations Regional Seminar on Census Data Dissemination and Spatial Analysis
Nairobi, Kenya, September, 2010