Why the Cook County Assessor’s Office made its residential assessment code and data public — voluntarily
By Robert Ross
Chief Data Officer, Cook County Assessor’s Office
Announcing that a County Property Tax Assessor is releasing the source code for their Computer Assisted Mass Appraisal system is a bit like saying you prefer Star Wars to Star Trek; 99% of your audience will be confused and bored while 1% will be apoplectic.
Last night, in front of a packed, sold-out crowd at Chi Hack Night–the city’s weekly gathering of coders journalists, academics, and civic technologists, the Cook County Assessor’s Office unveiled an unprecedented transparency initiative, and it matters far more than your preference in science fiction.
Assessor Kaegi and I pushed the code live by selecting an audience member at random to join our presentation and hit the publish button, symbolically demonstrating the nature of our work as by, for, and of the citizens of Cook County.
The Cook County Assessor estimates the fair market value for hundreds of thousands of residential properties each year. It does this mostly through algorithms that leverage data on sales and property characteristics.
Until now, these algorithms and data were kept confidential, released only via FOIA request or court order. This made it very difficult to monitor the performance Assessor’s Office. Are assessments fair? Are they consistent? Without the underlying data, these and other questions simply go unanswered.
The CCAO published its code and data on GitLab, an open-source online platform for software development, as well as the Cook County Open Data Portal. Publishing the code on the Data Portal is part of the CCAO’s ongoing partnership with the Cook County Bureau of Technology.
This new system for publishing and updating code will allow journalists, academics, and the public to monitor our performance, and even suggest changes to our methods that can improve our accuracy. Transparency in civic technology is a two-way street.
By using the same git version control system developed for Silicon Valley tech firms, we can achieve an unprecedented level of transparency in policy. Every change to the code is recorded, and the state of the code is preserved.
To our knowledge, no other Assessor’s Office in the United States does this. We hope that this initiative can serve as a test case and a blueprint for other offices that use computer algorithms to enact policy. We believe that, if our code is good enough to use to produce tax assessments, then it is good enough to be made public.
Our next data project is a legislative one: the passage of SB 1379, the Data Modernization Bill. This bill would gives the Cook County Assessor’s Office (and other Illinois counties who opt-in) the ability to collect operating income and expense data from income-producing properties. This would improve our models through better data, leading to fairer assessments. It would also create create neighborhood/market-level databases (which would be anonymized to prevent the release of proprietary information) of rents, cap rates, vacancies. Knowing this information would spur investment, improve our work, and be an example for others to follow.
SB 1379 recently passed the Illinois Senate in a bi-partisan vote of 36–16–1. Its next step is the Illinois House Revenue Committee then a vote in the full House.
In closing, I’m giving my boss, Assessor Kaegi, the final word:
“We have some long-term technological challenges to overcome in our office, but we haven’t let them stop us from innovating wherever we can, particularly when it comes to transparency.”
RESOURCES
Photos and documentation of public code release at Chi Hack Night:
https://twitter.com/AssessorCook/status/1118293162659844102
Data narrative (via the Cook County Open Data Portal):
https://datacatalog.cookcountyil.gov/stories/s/p2kt-hk36
Modeling Data:
https://datacatalog.cookcountyil.gov/Property-Taxation/Cook-County-Assessor-s-Modeling-Data/5pge-nu6u
Assessment data:
https://datacatalog.cookcountyil.gov/Property-Taxation/Cook-County-Assessor-s-Assessment-Data/bcnq-qi2z
First Pass Values:
https://datacatalog.cookcountyil.gov/Property-Taxation/Cook-County-Assessor-s-First-Pass-Values/x88m-e569
Full code base on GitLab:
https://gitlab.com/ccao-data-science---modeling/ccao_sf_cama_dev
