Statistical Analysis & Dissemination of Census Data

1. Statistical Analysis & Dissemination of Census Data UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

2. Statistical Analysis and Dissemination of Census Data • Outline • The Power of Maps • Introduction and Example • Dynamic Census Atlases • Overview & Example • Spatial Analysis Techniques • Overview & Examples • Digital Geographic Data for Dissemination • Overview & Cost and Benefits • Digital Data Dissemination Strategies and Users • Overview of Users UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

3. Anyone or anything can be associated with a known location in the world UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

4. CHILE: HOUSING AND POPULATION CENSUS DISTRICTS 2002 UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

5. Tsunami Affected Areas in Gizo, Solomon Islands UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

6. The power of maps • Maps communicate a concept or an idea. • Maps are often meant to support textual information • Maps appeal to the viewer’s curiosity • Maps summarize large amounts of information concisely • Maps can be used for description, exploration, confirmation, tabulation • Maps encourage comparisons: • Between different areas on the same map: where are population densities highest? • Between different maps: is child mortality higher in the districts of province A than in province B? • same area: where and by how much do literacy rates for males and females differ in the districts? • Between maps for different time periods: did fertility rates decline since the last census? UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

7. Dynamic census atlases • Alternative to a static census atlas • Publishing of a digital map and database together with mapping software can allow users to produce custom maps of census indicators. • Normally includes digital boundary files at a lower resolution than the full census database to allow fast drawing and low disk usage • closely integrated attribute table should contain only a selected number of census indicators. • Densities and ratios that are appropriate for mapping should already be calculated. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

8. Dynamic census atlases • The data provider should therefore provide an easy-to-use package together with the boundaries and data. • The use of that package should require minimal training and experience. • The application should be “plug-and-play”—after installation, the user should immediately be able to produce maps • Drill-down options for different geographic selections • Interactive area delineation options (e.g. select schools in a district) UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

9. A screenshot of Ukraine’s dynamics census atlas UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

10. Spatial Analysis Techniques • the main use of spatial analysis is for census products and services • Techniques include: 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. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

11. Spatial Analysis Techniques • Some prevalent forms of spatial analysis especially useful for use with population data include: • Queries • Distance measurements • Transformations • Buffering • point-in-polygonanalysis • Polygon overlayanalysis UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

12. Spatial Analysis Techniques • Queries: • Often this is the first step in an analysis, where one seeks to create a subset of units such as populated places with certain characteristics, allowing the user to check how typical an observation is against other observations • They use a GIS program to answer simple questions posed by the user, with no changes in the database and no new data produced. • An example of a query using geocoded census data is, select all towns with a population greater than 1,000 persons. These towns can then have their attributes summarized, for instance, to measure their total fertility rates against smaller towns and villages, then map the results • The term exploratory data analysis refers to investigations of patterns and trends in data using such techniques as querying UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

13. Area delineation • E.g. Interactive determination of school districts with the same number of children in each school grade by aggregating census dissemination areas UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

14. Spatial Analysis Techniques • Distance measurements • Easily done with all GIS programs, using the centroids (or center points) of cities, towns, and villages. • An analysis can be done to select villages located more than a kilometer from a school, clinic, or water source. • These can then be further analyzed using the attribute information for the populated places themselves. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

15. Spatial Analysis Techniques • Transformations • Methods of spatial analysis that use simple geometric, arithmetic or logical rules to create new datasets • Transformations can include operations that convert raster into vector data, or a stream of GPS coordinates into a route or a boundary • Of all the transformational techniques, buffering is the most well known and important UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

16. Spatial Analysis Techniques • Buffering (transformation) • Involves building a new data layer by identifying all areas that are within a certain specified distance of the original. • Buffering can be performed on points, lines and polygons and can be weighted by attribute values. • Buffering can be used to model travel time, for instance, by creating a “catchment area” around a particular feature such as a school or a clinic. • This provides a measure of accessibility that can be mapped across the extent of a country. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

17. “is near to”: Buffer Operations • Point buffer • Affected area around a Hospital • Catchment area of a water source UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

18. Buffer Operations • Line buffer • How many people live near the polluted river? • What is the area impacted by highway noise? UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

19. Buffer Operations • Polygon buffer • Area around a reservoir where development should not be permitted UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

20. Spatial Analysis Techniques • point-in-polygonanalysis • Determines whether a point lies inside or outside a polygon. • Can be used to compare geocoded village centroids lying inside and outside hazardous areas such as tropical storm tracks or earthquake zones. • Polygon overlayanalysis • 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 UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

21. Spatial Analysis Techniques • Spatial interpolation • A spatial analysis method designed to fill in values that lie between observations • A variety of methods including inverse-distance weighting and kriging are used to estimate the values of unsampled sites • based on Tobler’s first law that all nearby objects are more similar than distant objects • Kriging: interpolation technique for obtaining statistically unbiased estimates of spatial variation of known points such as surface elevations or yield measurements utilizing a set of control points • In kriging, the general properties of a surface are modeled to estimate the missing parts of the surface UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

22. Example of linear interpolation creating contours UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

23. 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. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

24. Areas of influence • Commuting distances: daily commuters flow UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

25. Spatial Analysis Techniques • Descriptive summariesare aspatial equivalent of descriptive statistics (such as mean and standard deviation) that represent the essence of a dataset in 1 or 2 numbers • Centersof population are the two-dimensional equivalent of a statistical mean and are often used to display the center of population using the weighted average of x and y coordinates of populated points • Point pattern or cluster analysis regards the distribution of points in space irrespective of their actual locations to determine whether patterns are random, clustered, or dispersed • hot spots are where high values are surrounded by high values, or cold spots, where low values are surrounded by low values. These are particularly useful for identifying populations at risk as well. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

26. 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 UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

27. Modelling: smoothing • Evolution of the population beetwen two censuses UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

28. Digital Geographic Data for Dissemination • Demand for digital databases that consist of extractions of the census agency’s digital geographic master database will only increase • Census data are an important input in policy planning and academic analysis in many fields. • Health service provision, educational resource allocation, design of utilities and infrastructure, and electoral planning are some applications where government agencies require spatially referenced small area population statistics. • Commercial users employ such data for marketing applications and location decisions. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

29. Digital Geographic Data for Dissemination • Benefits and costs • Benefits: Unsurpassed detail and precision, the potential use of census data in numerous applications--especially when overlaid on other geographic data such as terrain, and the relative ease of management and storage of thousands of units • Costs:expense in processing and data management, possible data disclosure issues, and quality control;costs of metadata production should be factored into the equation as well UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

30. Digital Data Dissemination Strategies and Users • The wide range of potential users of disaggregated census data means that the NSO needs to pursue a multi-leveled digital data dissemination strategy. • Broadly, we can distinguish between the following types of users: • Advanced GIS users • Computer literate users • Novice users UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

31. Digital Data Dissemination Strategies and Users • Advanced GIS users • work easily with large datasets and can use ftp to access them • Require extensive metadata. Sometimes called data extractors or “power users” • They will want access to spatial and attribute information in a comprehensive digital geographic format • The census office needs to supply comprehensive documentation on the geographic parameters used for the geographic database as well as on the individual census variables • The spatial information will be distributed in an open geographic format that can be easily converted into any number of commercial GIS formats UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

32. Digital Data Dissemination Strategies and Users • Computer literate users • Government, commercial or private sector users who want to be able to browse the thematic information in a census database spatially. • Want to produce thematic maps and thus need to be able to perform simple manipulation of cartographic parameters. • Simple analytical functions such as aggregation of census units to custom-designed regions should also be possible. • This group of users is best served with a comprehensive, pre-packaged application that is designed for a commercial or freely available desktop mapping package. • Documentation requirements are somewhat smaller, since the users are unlikely to change the geographic parameters of the database or perform more advanced GIS operations. UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

33. Digital Data Dissemination Strategies and Users • Novice users • Largely want to view pre-prepared maps on a computer and perhaps perform some basic queries • Best data distribution strategy is often to produce a self-contained digital census atlas • This atlas could consists of a series of static map images, for example, in the form of a slide show • Or it could be a very simple mapping interface with pre-designed map views that allow basic queries • Both, static maps and a simple map interface, can be made accessible through the Internet UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round

34. GRACIAS POR SU ATENCIÓN UNSD-CELADE Regional Workshop on Census Cartography for the 2010 Latin America’s census round