Idaho local data guide

How the Community Planning Association of Southwest Idaho (COMPASS) Forecasts Population

The Community Planning Association of Southwest Idaho (COMPASS) distinguishes between population estimates and demographic forecasts to guide regional planning. While annual estimates provide a snapshot of current growth using building permits and Census data, demographic forecasts look decades ahead to model future needs for housing, employment, and transportation infrastructure in Ada and Canyon Counties.

Updated with grounded research as of 2026-09-04.

The short answer

COMPASS does not forecast population using a single static calculation; instead, it develops demographic forecasts through a collaborative process involving the COMPASS Demographic Advisory Workgroup. These forecasts are integrated into the COMPASS Travel Demand Model, which simulates how future populations will travel and interact with regional infrastructure. While population estimates (used to track current growth) rely on a mathematical formula involving Census baselines and building permits, forecasts are strategic projections intended to support long-range planning documents, such as the *Communities in Motion* vision.

Key facts

Population Estimate Formula
Population = [Census Baseline] + ([New Residential Units Permitted] × [Average Household Size] × [Residential Occupancy Rate]).
Forecast Scope
Demographic forecasts typically project 25–30 years into the future and focus on Ada and Canyon Counties.
Primary Purpose
Forecasts serve as a foundation for the regional long-range transportation plan, *Communities in Motion*, and help guide land use and infrastructure decisions.

Estimates vs. Forecasts

It is important to distinguish between how COMPASS reports current numbers and how it plans for the future. Population estimates, released annually, are designed to track the past and present. They act as a pulse check on regional growth using actual, ground-level data like building permits, city annexations, and vacancy rates.

In contrast, demographic forecasts are scenarios used for planning. These are not intended to predict an exact date-specific number but rather to provide a reasonable estimate of where people, jobs, and houses will be in the coming decades. This helps planners avoid surprises by ensuring the transportation network can accommodate anticipated shifts in regional development.

The Forecasting Process

The forecasting process is collaborative and data-driven. COMPASS works with a Demographic Advisory Workgroup to ensure that assumptions regarding birth rates, migration, and economic trends are reasonable and reflective of local realities.

Once a total regional population forecast is determined—such as the 1.3 million projected for Ada and Canyon Counties by 2055—COMPASS staff allocate that growth across the region. This allocation considers existing development patterns and public input, ensuring the infrastructure investments recommended in *Communities in Motion* align with how the region is actually growing.

Why These Forecasts Matter for Residents

For those making relocation or housing decisions, understanding these forecasts provides insight into long-term regional development. COMPASS data informs more than just roads; it influences how member agencies plan for utilities, schools, and land use, which directly affects local quality of life.

Because these forecasts are updated periodically to reflect changing economic conditions and infrastructure progress, they offer a moving picture of the Treasure Valley’s future rather than a fixed one.

Common questions

How do population estimates differ from U.S. Census data?

U.S. Census data is a complete count of the population taken every ten years [1.3.7]. COMPASS population estimates are calculated annually to bridge the gap between those decennial counts, using local building permits and occupancy data to account for growth between Census years.

Are COMPASS forecasts reliable for rural areas?

COMPASS demographic data focuses primarily on Ada and Canyon Counties. While the organization may collect data for surrounding areas like Boise and Elmore Counties, the detail and accuracy of these forecasts can vary significantly compared to the metropolitan areas where more robust building permit and municipal data are available.

Related Idaho questions

  • What is the Communities in Motion long-range plan?
  • How can I access COMPASS open data?
  • How does growth in the Treasure Valley impact local infrastructure?

Sources and verification