---
id: engines/populationsim
about:
  label: PopulationSim
  description: >-
    Open-source population synthesiser in the ActivitySim family that builds
    household and person tables for a region from a census sample and local
    control totals, as input to travel models.
  tags:
    - synthetic population
    - census
    - travel demand
    - activity-based model
    - Python
tool:
  form: open-source Python package with a command-line tool
  group: People and populations
  homepage: 'https://activitysim.github.io/populationsim/'
  licence: BSD-3-Clause
  cost: free
domains:
  - people
  - mobility
open:
  source: open
  data: unknown
  api: unknown
  participation: open
  licence: BSD-3-Clause
relations:
  - predicate: alternative_to
    target: engines/simpop
  - predicate: built_on
    target: engines/activitysim
provenance:
  origin: agent
  sources:
    - title: ActivitySim/populationsim (README)
      url: 'https://github.com/ActivitySim/populationsim'
    - title: PopulationSim documentation
      url: 'https://activitysim.github.io/populationsim/'
    - title: ActivitySim/populationsim LICENSE.txt
      url: 'https://github.com/ActivitySim/populationsim/blob/master/LICENSE.txt'
    - title: ActivitySim/activitysim (README)
      url: 'https://github.com/ActivitySim/activitysim'
    - title: Release v0.10.0 · ActivitySim/populationsim
      url: 'https://github.com/ActivitySim/populationsim/releases/tag/v0.10.0'
  created: '2026-10-23'
  reviewed: '2026-10-23'
  reviewed_by: 'Claude, from the sources listed'
  status: draft
---
A travel model often needs a list of every household in a region and the people in it, with their ages, incomes and jobs.[^2] Real lists of that kind are private. PopulationSim builds a synthetic one: an invented population that matches the published counts for each small area, so a model can hold "everyone" without holding anyone's records.[^2] It began with the Oregon Department of Transportation, which wanted a shared, open tool for statewide, regional and city transport planning.[^1,2] It is built on ActivitySim, the open activity-based travel model run by a consortium of metropolitan planning organisations and other transport agencies.[^1,4]

It needs two things. The first is a seed sample: real but anonymised household and person records, usually the US Census Public Use Microdata Sample (PUMS) or a travel survey, each with a starting weight.[^2] The second is a set of controls: totals from the census or from forecasts, such as households by size or people by age, for areas like block groups, traffic analysis zones or counties.[^2] PopulationSim adjusts the weights of the seed households until they add up to the controls at every level of geography at once, changing the starting weights as little as possible.[^2] It then turns the weights into whole numbers and copies each sample household that many times.[^2] The output is a household table and a person table for the region.[^2]

The same machinery can reweight a household travel survey to match control totals, produce cross-tabulated counts for older four-step travel models, or adjust an existing regional population for a smaller study area.[^2] It runs from the command line with a folder of configuration files and a folder of data, and the documentation includes a page on checking the results against the controls.[^1,2]

The result is only as good as its controls. Attributes that are not controlled are carried along from the sample households and are not matched to anything local.[^2] The code is BSD-3-Clause and active; the latest GitHub release is v0.10.0 from November 2025, while the documentation site still describes version 0.5.1.[^2,3,5]