Geographic Mismatch Error: Chicago Ward 9
Ward Geography vs. Census Geography
The map below shows how Census geographies correspond to Ward 9 boundaries in Chicago. Ward boundaries are shown with a solid black outline. The selected Census geography is shown with solid gray outlines; use the layer control to switch between Census tracts and the block-group/tract hybrid. Geographies that are partially inside and partially outside a ward are shaded in blue; the portion outside the ward is shown with orange striped shading. Demographic data from the outside portions is borrowed into the ward’s estimates and is the source of geographic mismatch error.
Map Key
Split tract — inside ward
Split tract — outside ward
Ward boundary
Tract boundary
Quantifying Geographic Aggregation Error
Using 2020 decennial census block-level data, the table below isolates the error caused by geographic aggregation. The true values come from direct aggregation of unaggregated census blocks into the ward boundary. The tract and hybrid estimates are then built from the same block data after first rolling those block counts up to census tracts or block groups, and then re-estimating the ward from those larger units. This shows the distortion introduced by using tract- or block-group-level geography instead of direct blocks. Because every figure comes from the same decennial census source, this comparison removes sampling noise and time mismatch and isolates the effect of aggregation alone.
| Variable | Direct Blocks (Decennial Census Data) |
Estimate (Block Data Aggregated Up)
|
Error (Estimate − True)
|
||
|---|---|---|---|---|---|
| Tract | Hybrid | Tract | Hybrid | ||
| Race | |||||
| Hispanic or Latino | 4.72 | 4.81 | 4.83 | +0.09 pp | +0.11 pp |
| White | 1.40 | 1.43 | 1.44 | +0.03 pp | +0.04 pp |
| Black | 91.38 | 91.22 | 91.22 | -0.16 pp | -0.15 pp |
| Asian | 0.10 | 0.12 | 0.11 | +0.02 pp | +0.01 pp |
| Other or Multi-racial | 2.41 | 2.42 | 2.39 | +0.01 pp | -0.02 pp |
| Average Absolute Error | — | — | — | 0.06 pp | 0.07 pp |
| Age Group | |||||
| Under 5 years | 5.82 | 5.75 | 5.78 | -0.07 pp | -0.04 pp |
| 5 to 17 years | 17.19 | 17.34 | 17.16 | +0.15 pp | -0.03 pp |
| 18 to 24 years | 8.92 | 9.09 | 9.02 | +0.16 pp | +0.10 pp |
| 25 to 44 years | 24.11 | 24.09 | 24.08 | -0.02 pp | -0.03 pp |
| 45 to 64 years | 26.02 | 25.96 | 26.13 | -0.06 pp | +0.10 pp |
| 65 years and over | 17.93 | 17.77 | 17.83 | -0.17 pp | -0.10 pp |
| Average Absolute Error | — | — | — | 0.10 pp | 0.07 pp |
| Housing Tenure | |||||
| Owner-occupied | 49.55 | 49.34 | 49.71 | -0.21 pp | +0.16 pp |
| Renter-occupied | 50.45 | 50.66 | 50.29 | +0.21 pp | -0.16 pp |
| Average Absolute Error | — | — | — | 0.21 pp | 0.16 pp |
| Housing Occupancy | |||||
| Occupied Housing | 86.91 | 86.86 | 86.78 | -0.05 pp | -0.13 pp |
| Vacant Housing | 13.09 | 13.14 | 13.22 | +0.05 pp | +0.13 pp |
| Average Absolute Error | — | — | — | 0.05 pp | 0.13 pp |
| Household Size | |||||
| 1-person HH | 32.91 | 32.86 | 32.96 | -0.05 pp | +0.05 pp |
| 2-person HH | 26.71 | 26.67 | 26.73 | -0.04 pp | +0.01 pp |
| 3-person HH | 16.83 | 16.99 | 16.83 | +0.16 pp | +0.00 pp |
| 4+ person HH | 23.55 | 23.47 | 23.48 | -0.08 pp | -0.07 pp |
| Average Absolute Error | — | — | — | 0.08 pp | 0.03 pp |
| Household Type | |||||
| Family Households | 62.58 | 62.54 | 62.41 | -0.04 pp | -0.17 pp |
| Married-couple Family | 19.79 | 19.68 | 19.76 | -0.11 pp | -0.03 pp |
| Non-family Households | 37.42 | 37.46 | 37.59 | +0.04 pp | +0.17 pp |
| Living Alone | 32.91 | 32.86 | 32.96 | -0.05 pp | +0.05 pp |
| Average Absolute Error | — | — | — | 0.06 pp | 0.10 pp |
| Average Absolute Error Across Categories | — | — | — | 0.09 pp | 0.09 pp |
| Note: Percentages may not sum to 100% due to rounding. | |||||
| Average Absolute Error: mean of absolute errors across variables within each category. | |||||
| Average Absolute Error Across Categories: simple average of the six category-level averages. | |||||