Tenant Power uses city assessor's data from Boston, Cambridge, Somerville, Medford, and Brookline, Massachusetts to identify additional properties that are likely owned by your landlord. We're able to make pretty good guesses! But this data can only tell us so much---we encourage you to check Massachusetts Land Records and/or the assessors databases linked above to confirm ownership.
Tenant Power uses what is called 'supervised machine learning' to assess whether properties have the same owner; we use the owner's name, co-owner's name, and owner's address to identify likely matches. Basically, this means that we used our judgement to decide whether a few hundred property pairs were owned by the same entity; an algorithm then used our 'training' dataset to decide which of the remaining 200,000+ properties were owned by the same entities.
This approach is powerful, but far from perfect. It means that we're reasonably good at identifying shared owners when these fields are shared; it also means that we're liable to mis-identify duplicates where these fields nearly match. It's also frequently the case that property owners use multiple business names to mask their activities. If these do not share an address, we have no way of identifying them.
We built the web application using Mapbox, node.js/Express, and PostgreSQL/PostGIS. All our code is available on Gitlab: the web application, as well as the deduplication process and data scrapers (the latter is in R). Deduplication is facilitated by the dedupe Python library.
If you'd like to get involved (come one, come all!), send an email to email@example.com.
Tenant Power uses city assessor's data from Boston, Cambridge, Somerville, MassGIS (Medford), and Brookline. Brookline has not filed new assessor's parcels with MassGIS since 2011 and do not make their parcel data transparently available. For this reason, we scraped current parcel data for Brookline from a map application made available by the city.