Fairfax County’s Open Data GIS system makes several large datasets covering parcels within the county available to the public. The datasets must be combined using statistical software before they can be analyzed. For this project the relevant data are included in two datasets:
- Legal data: https://data-fairfaxcountygis.opendata.arcgis.com/maps/tax-administrations-real-estate-legal-data/about
- Assessed Values: https://data-fairfaxcountygis.opendata.arcgis.com/datasets/Fairfaxcountygis::tax-administrations-real-estate-assessed-values/
These datasets are imported with irrelevant columns being dropped on import. They are then merged together using a pandas left join on the common column, PARID, which pandas auto-selects. Missing values from the assessed values columns are then dropped:
pd.merge(legal, assessments, how='left').dropna(subset=['PRITOT', 'APRTOT'])This results in a dataset with 364,691 unique parcel ids which include apraisals for 2021 (PRITOT) and 2022 (APRTOT).
Next the tax data must be fetched. This can be downloaded from the Fairfax County website in PDF form. To convert to machine-readable format the data was converted to an HTML page by Adobe Acrobat DC, then the HTML was copy/pasted into Microsoft Excel followed by some minor cleaning:
- removing multiple header columns
- TOTAL TAX label being added to blanks under ‘FUND NAME’
- converting the tax rate from percent to decimal
- water_fee being added to the few relevant areas with copy/paste
Once the data is ready for pandas in a tidy csv file, it can be imported and the tax rate column filled in using drop_duplicates to isolate the tax rate, then a merge to fill in the blanks on the main dataset. This also has to be done for the refuse fee and those districts who do not have additional fees need to have refuse fee and water fee filled with zeros.
To find the total tax for the database, multiply the APRTOT by 2022 tax and add water fee and refuse fee columns, then do the same for 2021 and PRITOT. Then column-wise summations and other calculations can be made.
Property Taxes for all of Fairfax County: 2022: $3,798,869,215.82 2021: $3,596,410,513.71 difference: $202,458,702.12 Percent change: 5.63%
The county collected about $3.8 billion in 2022, compared with $3.6 billion in 2021. An increase of 5.63%.