Small Area Statistics (Tiny, tricky geographies, and the people who need them)
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Transcript of Small Area Statistics (Tiny, tricky geographies, and the people who need them)
Small Area Statistics
(Tiny, tricky geographies, and the people who need them)
Geography
Geography and Statistics: the ‘Where”
There’s always a ‘where’ (+ time + variables)
The importance of the where varies depending on what you’re examining
Like statistics, ‘where’ displays often spur new ‘why’ questions
Why learn about small area stats?
Small area statistics: are essential for certain types of
analyses can be challenging to find, understand
and to work with; can answer local and very specific
questions can be expensive to produce and
obtain (i.e. present access challenges)
Small Area StatisticsObjectives today - to build understanding of: The relationship between geography and
statistics The terminology and hierarchical structure of
Census geography, to understand commonly accessible smaller units
Other small geographical units important to statistical display which are important/frequently requested
How to use key Statistics Canada tools to find or generate spatial display of statistics
What are ‘small area statistics’ about?
High demand for information at the ‘lowest geographic level available’
Statistics at sub-provincial, or sub-municipality level, are critical to analyses of: health (e.g. spread of disease), housing, crime, social issues (e.g. emerging patterns of
concern or interest), emergency preparedness (analysis of this doesn’t work
at a whole-municipality level), market analysis, (why do they want my postal code
anyway?) and much, much more!
Privacy and confidentiality
Keeping the unit of analysis anonymous is a challenge with small area information (if one has good local knowledge, you can identify a person)
There are rules in place about what population counts are required in order for small area statistics to be released (e.g. income)
Expense and access
Authoring agencies, because of budget limitations, (‘priorities’) are always balancing availability of variable detail and finer levels of geography
Expense and Access
More variables? > $$$
Smaller geography? > $$$ !!
No access/distribution infrastructure in place
Simply not available or collected
Geographic display
What can a map display do that a listed table cannot? Summarize the big picture – with a picture Rapidly show PATTERNS of disparity that might have
some unexpected explanation Allow display of statistics without knowledge of coding
structure for viewers
Brief words on: why Geographic Information Systems?
Small area statistics are not easily read in tables Graphic display becomes much more important at
smaller levels GIS increasingly used as a tool for small-area
analysis and summary
John Snow’s Cholera Map
No need to label the areas: the image says enough
Geographic displays of stats always involve choices, too Simple shade of color choices imply different
meanings Ranges of statistics (‘breaks’ in the data) can be
manipulated to imply different things Statistics can be left out of maps easily; what is
missing? Source statistics may be ‘bad’
Sierra Club: Deforestation
Geographic displays of statistics are subject to metadata review Evaluation of an online map display is as required
as an evaluation of statistics via metadata review; metadata criteria also apply to maps (sources should be cited, survey specified; see yesterday’s slide)
The Census Geography Hierarchy
Organizing a national system of statistical reporting depends on a full-coverage nested geographic hierarchy; i.e. geography/GIS for StatsCan is about more than making maps
The hierarchy helps to ensure 100% coverage of the population during Census collection by organizing the country’s geography
The hierarchy also defines ‘level’ of the release of statistics
Small area statistics exist at the ‘bottom’ (yet $$) end of the hierarchy
The Statistics Canada Hierarchy
Great StatsCan Geography Tools for understanding hierarchy
Nice quick tutorial: http://geodepot.statcan.ca/Diss/Referenc
e/Tutorial/HC_tut1_e.cfm
Fantastic glossary: http://geodepot.statcan.ca/Diss/Reference/COGG/Index_e.cfm
A brief hierarchy overview
All levels of the hierarchy have definitions and corresponding codes Eg. Canada – 00; Alberta (Province) – 48
The levels and codes have defined relationships Below provinces, we have Census Divisions: eg 4801 Below provinces, Census Metropolitan Areas and Census
Subdivisions Below those, Census tracts and Dissemination Areas
(SMALL AREA STATISTICS)
Hierarchy continued
Hierarchy is defined administratively (ie political decision) and statistically (ie StatsCan’s reporting requirements)
Not everything in the hierarchy relates to every other unit (see chart); i.e. not a straight, linear hierarchy
Eg. Forward Sortation Areas “Odd” units (to StatsCan): ‘Designated Places’
Hierarchy applied to statistics
Not all statistics are available for all levels of the hierarchy; parts of the hierarchy may not exist in some places
Statistical analysis is more appropriately applied to some units than to others: eg. CMA vs CSD
Hierarchy and Small Area Statistics
What are the important small area statistics in the hierarchy?
Most commonly: Census Tracts and Dissemination Areas
Other small-area data units
What people want re: geography is often not the unit of geographic availability
Data typically compiled into statistics to meet the needs of the authoring organization
Who ELSE cares about these areas/what demands are in place for this information?
Solutions are available! (We’ll look at some)
Neighbourhoods
Frequent need for statistics at this level of geography
Census tracts vs. neighbourhoods Municipalities: purchasing profiles and sharing
agreements
Postal Codes
Frequently requested for market analysis/business applications
Represented graphically by dots in a product called the Postal Code Conversion File (PCCF)
Postal codes are regions! The PCCF allows matching of postal codes to the
best corresponding dissemination area
Roads and their attributes
“Unavailable” Statistics Canada geographic areas
Some data resellers ‘impute’ or calculate estimates of ‘missing data values’ for small area statistics
GeoSuite: Walk-Through Exercise
Click-along with Leah!
Exercise: Explore the hierarchy and statistics for your favorite geographic area using StatsCan Tools
Start here: http://geodepot.statcan.ca/Diss/Maps/Maps_e.cfm
Explore the three sources available and evaluate them for usability, metadata, and for what information they have to offer you:
What were you able to discover about your chosen area from each source?
To what level of geography were you able to reach using each source?