Learn how mySidewalk processes data for modern and custom geographic boundaries through apportionment and harmonization. This guide explains why data in mySidewalk may differ from other sources and provides tips to ensure accuracy.
Why Data in mySidewalk Might Differ from Other Sources
Data discrepancies can occur for two main reasons:
Dynamic calculation for custom boundaries (apportionment)
Harmonization of historical data into modern boundaries
1. Dynamic Calculation of Data for Custom Boundaries (Apportionment)
When you upload or draw a custom boundary in mySidewalk, the platform calculates data using these key elements:
Census Block Ratio Tables: Provides population, household, and housing unit ratios for each block.
Census Block Groups or Tracts Data: Used if block group data isn’t available.
mySidewalk then looks up all the Census blocks contained within your custom boundary, and finds the population, household, or housing unit ratio from those blocks to apportion values from the Census block group or tract into your custom boundary.
Why Use Census Blocks?
Census blocks offer more precise data by reflecting uneven population distribution. Factors like parks, industrial areas, and retail spaces impact how data is distributed within a block group or tract.
Population, Households, or Housing Units?
Most Decennial Census and ACS data fall into one of these three categories: population, households, or housing units. A household is a group of people living together, whereas housing units describe the physical structures where people reside. mySidewalk maintains a metadata system that tracks the best-fit ratio type for each case.
Pro Tip: For improved accuracy, ensure your custom boundary overlaps at least 40 Census blocks or 3 different Census block groups/tracts. Otherwise, a warning will be displayed.
2. Harmonization of Historical Data into Modern Boundaries
mySidewalk uses the latest geographic boundaries and recalculates historical data to fit them. This ensures consistency across datasets, even as boundaries evolve over time.