A Bird's Eye View

4. Measuring Density

What is the density of the street you live on? The answer is not any one number but several, depending on how you measure density and how broad an area you include in your calculation. Density can be expressed in different ways-persons per square mile, units per acre, or floor area ratio. Residential density is typically expressed in housing units per acre and measured as net or gross. Commercial or mixed-use density is more accurately expressed as a floor area ratio. The density of your "street" will depend on how you define the boundaries. Does it include the apartment building on the other side of the block? If so, the number will bump up. Are you including park on the next block? The number will drop.

For step-by-step instructions on how to measure density using the US Census online click here.

These images shown below should be layered in sequence so that the line jumps around and the captions change but the photograph stays the same. Here's an example of how density numbers can vary. Click on the image to see how varying the measurement area affects the density level.

The Back Bay of Boston has a density of 30 units per acre if a park along the river and an urban boulevard are included in the calculation.

Leave out the riverfront park and the number rises to 37 units per acre.

Focus on a smaller area of the Back Bay and the density is much higher-70 units per acre.

A close-up view shows the high-rise apartment buildings that give this section of the Back Bay a higher density than surrounding blocks.

Next 5. What Does Density Look Like? >>

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