For projects built prior to 2019, a list of proposed additions and new non-residential projects was generated from the Chester County Planning Commission's permit data for projects proposed from 2010-2019. The data included year proposed, location, description, non-residential type (agricultural, commercial, industrial, or institutional), and square feet. Assessment data was then used to determine the construction year for the permit data. Projects were assumed completed when significant changes in assessment value were recorded. Historical Google aerial imagery was then used to confirm completion of projects with assessment change and identify additional completed projects. Approximate years were assigned for built projects when the exact construction year was unavailable on aerial imagery. All other projects were assumed to remain incomplete.

For 2019 through 2020 new non-residential building data, an annual permit data list was generated for projects proposed in the previous year and added to the list of outstanding projects. The identified projects were then sent to municipalities for review. Finally, site visits were completed to ascertain status of any projects that did not receive municipal review.

For 2021 and 2022 followed the prior years' process, with an addition of utilizing Nearmap imagery to determine completed projects. Because the latest available imagery was from October 2021, any projects which were partially built in the imagery were reviewed by site visits in February 2022.

For projects over 10,000 square feet prior to 2021, aerial imagery was cross referenced with the approved building plans to obtain updated building square feet added. For 2021 and 2022 projects, any changes for all projects from original plans were noted and square footage was adjusted using measurement tools in Nearmap. If final building matched the original plan, the submitted square footage was used.

Building type was obtained through submitted plan data, and updated as needed. Projects with more than one building type were counted as .5 of a project.

Due to the methodology changes, data from prior years may have changed due to previous inaccuracies in completion status.