Community Resource Guide

table of contents

Basic Building Information

  • Tax Lot Identifier (BBL)

BBL stands for borough, block, lot. It is a 10 digit tax lot identifier. The first digit represents the borough, the next five the block, and the last four the lot. Many city datasets are organized by BBL - it is the most commonly used way to identify buildings throughout the city.




The Bronx     






Staten Island     


Below is a screenshot of the OASIS Map website showing the tax lot map for the area around the UNHP office. The block number is indicated in red. The lot numbers are indicated in black. The office is located in the Bronx, so the first digit of the BBL is 2. The block is 3315. As this is only a four digit number, we will add a leading zero when writing out the BBL. The building is marked as lot 1 - we will add three leading zeros to this to achieve a 4 digit lot value. This gives us a BBL of 2033150001.

In most cases, there is only one building per BBL (one building on the actual lot); however this is not always the case. With NYCHA properties, for instance, all of the buildings in a particular development will have the same BBL. When there is more than one building per BBL, you can distinguish between them with the BIN number. If you do determine that there are multiple buildings within the same tax lot, you will need to decide if you want to try to treat the buildings differently or as a unit. Importantly, if there are multiple buildings within one lot they will have the same owner. One thing to consider here is that much of the available data does not include BIN information, rather it will only have BBL level information.

You can look up a building’s BBL in a few ways. One option is to use the DOF BBL Lookup site. Click ‘Property Address Search’ and enter the address you are interested in. The search results will include the BBL in the top right hand corner. You will also be able to see who is on file as the owner of the property as well as the property’s tax bills. We will explain how to understand this additional information later on. Another way to find a building’s BBL is to use the OASIS Map website. Search for the address you are interested in, then click on the ‘Location Report’ tab on the right. In addition to returning the BBL, OASIS Map will tell you the number of buildings on the tax lot, the number of units in the building, and the political districts that the building falls within. Additionally, the website provides links to other useful websites we will discuss later such as ACRIS, HPD, DOB, and DOF. There are also many data tools that have been developed that enable you to search by address - more on this in the Tools for Building Research section.

  • Building and Internet Searches

Another good way to get some basic information about the building is to see if you can find previous reporting on it, or if the owner has been included on any watch lists. In other words, look to see what information you can find on the internet beyond what is available on city sites. There are a few angles and sites we recommend checking which we will outline below.

  • Helpful Keywords: tenants, landlord, organizing, issues

  • Reporting

Search the building address and check if it is mentioned in any articles. Have there been previous organizing drives in the building? What issues were the tenants facing then? Has there been a change in ownership since? Have many of the original tenants left the building?

  • Streeteasy & Zillow

These sites can be used to get an idea of what rents are like in a building. On both you are able to scroll down and look at past rentals. Even if there is no information available for individual units in the property, there will still be information about the building as a whole such as the number of floors, units, the year the building was built, and districting information.

While there is often only information available for a few of the units, you are able to see the size of the unit, when it was rented, and what the rent level was. This can help shed some light on the types of units in the building (studios, 1 beds, etc.) as well as what the rent levels have looked like over the years. Actual rent rolls are often very hard to find for a building unless it is being sold, this method allows you to start to estimate how much the landlord is collecting through the rent roll.

  • Google Maps

Google Maps has a history view feature where you can look at old street view images. This allows you to see what the exterior of the building has looked like over the years, starting around 2007 or so. You will be able to see if the building was developed recently, or if it looks like the exterior of the building has visibly deteriorated. You may also be able to get a feel for how the block around the building has changed - has a large, new development gone up? Was there scaffolding that suggested a major renovation?

To look back in time, search the building’s address and go to the street view. There will be a dark gray box in the top left corner. At the bottom of the box it will tell you the month and year that the photo is from. You can click on this text to toggle through the images that are available from previous years as highlighted by the red box in the image below.