2015 AHS Redesign Paper 4

Constructing Unit-Level Addresses in the 

Public and Indian Housing Information Center

Shawn Bucholtz

U.S. Department of Housing and Urban Development

Pramod Pamnani

Cloud Nine Technologies

March 2016

U.S. Department of Housing and Urban Development | Office of Policy Development and Research
Constructing Unit-Level Addresses in the 

Public and Indian Housing Information Center

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Constructing Unit-Level Addresses in the 

Public and Indian Housing Information Center

Purpose

The purpose of this paper is to summarize the process of constructing U.S. Department of Housing and Urban Development 

(HUD) public housing unit-level addresses. Unit-level addresses 

were constructed from building entrance addresses and door 

numbers contained within the Inventory Management System 

(IMS)/Public and Indian Housing Information Center (PIC) system and from information contained within HUD Form 50058. 

The project to construct unit-level addresses was undertaken 

because unit-level addresses are necessary for linking public 

housing administrative records to the American Housing Survey 

(AHS), the American Community Survey, and other data sources. 

1. Address Collection 

Background

This section provides background information on HUD’s tracking and classification of public housing units and on the address 

collection procedures. The purpose of this section is to show 

the reader that, although HUD does not require the collection 

of unit-level addresses in IMS/PIC, the IMS/PIC requirement 

to capture building entrance addresses, and public housing 

authorities’ (PHAs’) optionally choosing to enter extra information in the form of apartment numbers, results in a de facto 

collection of unit-level addresses for as many as 98 percent of 

public housing units. 

1.1 Public Housing Unit Tracking and 

Structural Classification

PHAs administer the public housing program. One system used 

to administer the program is called IMS/PIC. Within IMS/PIC, 

PHAs assign each unique public housing unit a key composed 

of four fields. 

1. Development code: A unique code for the housing development.

2. Building number: A unique number assigned to each physical 

structure within the housing development.

3. Building entrance number: A unique number assigned to each 

entrance of a unique physical structure (building).

4. Unit number: A unique number assigned to each unit within 

a unique building entrance.

Development code is generally synonymous with an apartment 

complex or a housing development. Building number is generally used to number each distinct physical structure (building) 

within an apartment complex or housing development. Building 

entrance number is used when a building has more than one 

entrance, such as a “north” and “south” entrance. Finally, unit 

number is assigned for each unit associated with a building 

entrance number.

This classification system was likely designed to facilitate the 

tracking of units within multifamily apartment complexes. 

Only about one-half of all public housing units, however, are 

located within what most people would consider to be multifamily apartment buildings or complexes. The other one-half 

are located within rowhouses or townhouses, duplexes, and 

single-family detached homes. This distinction is important for 

reasons that will become clear in the next subsections. Table 1 

shows the count of public housing units in each type of housing structure.

Table 1. Count of Public Housing Units by Structure 

Type, 2015

Structure Type Count of

Units

Percent of

Total Units

Multifamily apartment buildingsa 582,539 52

Rowhouses/townhouses 319,567 29

Duplexes 165,652 15

Single-family detached homes 46,446 4

Total 1,114,204 100

a

 The category multifamily apartment buildings includes two structure-type 

categories in the Inventory Management System/Public and Indian Housing 

Information Center, or IMS/PIC. The first is ES, which stands for structure with 

elevators. The second is WU, which stands for structures without elevators.

1.2 The Relationship Between 

Building Entrance Numbers 

and Unit Numbers

The four-field system for tracking public housing units ensures 

that each unit has a unique key that distinguishes it from all 

other units. For example, consider a public housing development (FL009) that structurally consists of one multifamily 
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apartment building. The building has two entrances, and each 

entrance has three units, for a total of six units within the building. The current coding/numbering scheme for the units would 

resemble the one described in table 2. As evidenced by table 2, 

all four fields are required to create the unique set of values 

necessary for tracking each unit in this multifamily structure.

Table 2. Example of Current Coding/Numbering Scheme 

for Units in Multifamily Structures

Development 

Code

Building

Number

Building Entrance 

Number

Unit

Number

FL009 1 1 1

FL009 1 1 2

FL009 1 1 3

FL009 1 2 1

FL009 1 2 2

FL009 1 2 3

Public housing units in rowhouses or townhouses follow 

the same coding/numbering scheme but with one important 

difference: each building entrance number has only one unit. 

In relational database parlance, this situation is referred to as a 

one-to-one relationship between the building entrance number 

and the unit number. To understand why, consider a public 

housing development (GA008) consisting of one building composed of six rowhouses. The current coding/numbering scheme 

for the units would resemble the one described in table 3. As 

evidenced by table 3, each of the first three fields (development 

code, building number, and building entrance number) are required 

to create the unique set of values necessary for tracking each of 

the six units, but the fourth field (unit number) is not strictly 

necessary because each building entrance is the entrance to an 

individual unit.

Table 3. Example of Current Coding/Numbering Scheme 

for Units in Rowhouses and Townhouses

Development 

Code

Building

Number

Building Entrance 

Number

Unit

Number

GA008 1 1 1

GA008 1 2 1

GA008 1 3 1

GA008 1 4 1

GA008 1 5 1

GA008 1 6 1

Rowhouses and townhouses comprise 29 percent of all public 

housing units. About 25 percent out of that 29 percent exhibit 

the one-to-one relationship between building entrance number 

and unit number illustrated in table 3. The other 4 percent maintain the one-to-many relationship between building entrance 

number and unit number that is found with units in multifamily 

structures (illustrated in table 2). No single explanation is likely 

as to why the one-to-many relationship exists for those 4 percent. 

One possible explanation is that the structure type truly is a 

multifamily apartment building but was incorrectly coded as a 

rowhouse/townhouse. Another explanation is that the structure 

type does not fit neatly into the structure type categories available in IMS/PIC, and the PHA simply picked the structure type 

category they believed most consistent with the structural layout.

Public housing units in duplexes generally have the same oneto-one relationship between the building entrance number and 

the unit number as is exhibited by units in rowhouses and townhouses. Table 4 shows an example of the coding/numbering 

scheme for public housing units in a development (IA004) consisting of three duplex structures, for a total of six units. Each 

duplex structure (building) has two entrances—one for each 

unit. Duplexes comprise 15 percent of all public housing units. 

As was the case with rowhouses and townhouses, each of the 

first three fields (development code, building number, and building 

entrance number) are required to create the unique set of values 

necessary for tracking each of the six units, but the fourth field 

(unit number) is not strictly necessary.

About 13 percent out of the 15 percent exhibit the one-to-one 

relationship between building entrance number and unit number. The other 2 percent maintain the one-to-many relationship 

between building entrance number and unit number that is 

found with units in multifamily structures.

Table 4. Example of Current Coding/Numbering Scheme 

for Units in Duplexes

Development 

Code

Building

Number

Building Entrance 

Number

Unit

Number

IA004 1 1 1

IA004 1 2 1

IA004 2 1 1

IA004 2 2 1

IA004 3 1 1

IA004 3 2 1
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As would logically be expected, public housing units that are 

single-family detached homes are coded/numbered as separate 

buildings. Consider the example in table 5 of a public housing 

development (MI002) consisting of six single-family homes. 

In this example, each physical structure (the single-family 

home) has a unique building number. As the example shows, 

one-to-one relationships exist between building number and 

building entrance number and between building entrance 

number and unit number. As such, each public housing unit 

that is a single-family detached home is unique based on only 

development code and building number; building entrance 

number and unit number do not provide any additional information that contributes to the uniqueness of the unit.

Single-family homes comprise about 4 percent of all public 

housing units. Virtually all of them exhibit the previously 

described one-to-one relationship between building number 

and building entrance number. 

Table 6 presents the total percentage of units by structure type 

and, within each structure type, the percentage of units that have 

a one-to-one relationship between building entrance number 

and unit number and the percentage that have a one-to-many 

relationship. In total, 44 percent of all public housing units have 

a one-to-one relationship between building entrance number 

and unit number. The importance of this feature of the public 

housing tracking scheme will become apparent in subsection 1.5.

Table 5. Example of Current Coding/Numbering Scheme 

for Units in Single-Family Detached Homes

Development 

Code

Building

Number

Building Entrance 

Number

Unit

Number

MI002 1 1 1

MI002 2 1 1

MI002 3 1 1

MI002 4 1 1

MI002 5 1 1

MI002 6 1 1

1.3 An Important Note About the Four 

Tracking Fields

As mentioned in subsection 1.1, PHAs track unique public 

housing units using a key composed of four fields with values 

assigned by the PHA: development code, building number, building 

entrance number, and unit number. Two important items are worth 

noting about these four fields as they relate to the address collection process discussed in subsection 1.5.

First, none of the four fields is designed to mimic how the U.S. 

Postal Service (USPS) assigns addresses to buildings within a 

multifamily property. It could be the case that HUD records a 

single building with four entrances, but USPS assigns all four 

entrances the same address (for instance, 123 Main Street). It 

could also be the case that HUD records a single building with 

four entrances, and USPS gives each entrance its own address 

(for instance, 123, 125, 127, and 129 Main Street).

Second, none of the four fields is required to contain numbers 

that correspond to actual street numbers or apartment numbers. 

In some cases, the unit number is an actual apartment number, 

but that is often the exception, not the rule. In short, the four 

fields are not required to contain, and often do not contain, 

actual address information.

1.4 U.S. Postal Service Address 

Definitions 

For the subsequent parts of this paper, especially subsection 

1.5, to be understood, some important terms must be defined.

• USPS Deliverable Address: An address recognized by USPS as 

a valid final delivery point for mail. In other words, an individual mailbox or a post office (PO) box. 

• Basic Street Address: The portion of an address that includes 

the street number and street name. For single-family homes 

and townhouses, the basic street address is often the USPS 

deliverable address or the PO box.

Table 6. Percentage of Public Housing Units With One-to-One Relationship Between Building Entrance Number and 

Unit Number

Structure Type Percent of

Total Units

Percent of Total Units With 

One-to-One Relationship Between 

Building Entrance Number and Unit Number

Percent of Total Units With 

One-to-Many Relationship Between 

Building Entrance Number and Unit Number

Multifamily apartment buildings 52 2 50

Rowhouses/townhouses 29 25 4

Duplexes 15 13 2

Single-family detached homes 4 4 0

Total 100 44 56
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• Full Address: The combination of basic street address plus 

any apartment, unit, or other identifier that is assigned by 

USPS. For most multifamily buildings, the full address is the 

USPS deliverable address.

1.5 Overview of Public Housing 

Address Information Collection

The previous subsections of this paper included necessary background material for understanding how PHAs record public 

housing addresses in IMS/PIC. Simply put, PHAs are required 

to collect building entrance number addresses. PHAs are not 

required to collect addresses at the unit-number level. 

PHAs collect actual physical address information for each building entrance number in the IMS/PIC. For each unit, the PHA 

may enter information in the following five fields.

1. address line 1.

2. address line 2.

3. city.

4. state.

5. ZIP Code.

Generally speaking, IMS/PIC has no check to ensure an address 

is a building entrance number address, nor any post-data-entry 

system that enforces address quality.

It is useful to pause for a moment and consider what the address requirements and entry process means for the different 

types of structures discussed in subsection 1.1. Nearly all 

single-family detached structures, duplexes, and rowhouses 

and townhouses exhibit a one-to-one relationship between 

building number and building entrance number, which means 

that building entrance number address functionally should 

be the unit address. In other words, even though recording 

addresses at the unit level is not required, unit-level addresses 

should exist for 44 percent of public housing units. 

The other 56 percent of public housing units exhibit a one-tomany relationship between building entrance number and unit 

number. Given the existing requirement to record only building 

entrance addresses, these addresses will definitely not be unit 

addresses. There is another data-entry field in IMS/PIC, however, called door number. This field is optional, meaning PHAs 

are not required to record any information in door number field. 

That being said, it is a logical place for PHA to record an actual 

apartment number for units with multiple unit numbers for a 

building entrance number. In fact, of the 56 percent of public 

housing units with a one-to-many relationship between building 

entrance number and unit number, 54 percent have some type of 

value in the door number field and 2 percent do not have a value.

That means PHAs are expected to have recorded unit-level address for 44 percent of public housing units and maybe to have 

provided enough information to construct a unit-level address 

for an additional 54 percent of public housing units. 

1.6 Potential Complications

As mentioned in subsection 1.5, PHAs potentially record unitlevel addresses for as many as 98 percent of public housing 

units, even though they are not required to do so. The IMS/PIC 

system does not have any internal checks, however, to ensure 

the building entrance addresses are recorded in a format that 

is consistent with postal address standards. The same thing is 

true for PHAs who have chosen to populate the optional door 

number field. 

In a data-entry system designed to ensure address entry consistency, PHAs would enter the basic street address in address 

line 1, the apartment number (as required when a one-to-one 

relationship exists between building entrance number and unit 

number) in address line 2, and the relevant city, state, and ZIP 

Code in their respective fields. PHAs, however, chose to enter 

the address information in numerous ways that are not consistent 

with that model. The following list includes a few examples.

• Address line 1 includes the house number, and address line 2

includes the street name (example: 5, Main Street).

• Address line 1 includes the basic street address, but address 

line 2 is missing an apartment number (example: 123 Main 

Street, null).

• Address line 1 includes the name of the subdivision, and 

address line 2 includes the full or basic street address 

(example: Dyson Homes, 123 Main Street).

• Address line 1 includes the full address, and address line 2

repeats the apartment number (Example: 123 Main Street 

Apt 101, Apt 101).

• Address line 1 includes a range of full addresses (Example: 

123–129 Main Street).

As a result, in some cases, the building entrance addresses are 

plagued with errors such that it is difficult to extract an address 

that is consistent with USPS standard. This situation is one in 

which address standardization and geocoding can help.
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1.7 Geocoding Process and Output

After collecting or updating building entrance address information in the online IMS/PIC system, HUD IMS/PIC database managers send the building entrance addresses to HUD’s Geocoding

Service Center (GSC). Using the building entrance address 

information, the GSC completes the following steps.

Step 1. Fix common HUD-specific address entry mistakes 

using internally developed software/code.

Step 2. Conduct address standardization and a deliverability 

assessment using commercial software (CODE-1 Plus®).

Step 3. Estimate the physical location of standardized address 

using commercial software (GCP 5.2).

Many address entry errors or nonstandard inputs will cause the 

geocoding process to return a null result or return a result with 

less precision than desired. The HUD GSC has developed an 

inventory of common address entry errors and corresponding 

procedures to correct the errors. These procedures are implemented in step 1. Because HUD deals with addresses throughout the country, this process must be somewhat conservative 

so that fixing systematic errors in one county does not create 

errors in other counties (false positives). As a result, GSC is 

unable to correct some addresses.

GSC’s commercial geocoding software’s address standardization 

process (step 2) is designed to fix common formatting errors. 

For instance, the software recognizes that a “#205” input should

be “Apt 205,” but it cannot handle truly messy formatting errors.

The output of the address standardization is an address that can

be used for step 3. It is entirely possible that the address standardization fails, however, resulting in null output. It is also 

possible that the address standardization removes information 

supplied by the user to signify an apartment number. For instance, if the user supplied “123 Main St #%204,” the software 

may return “123 Main St,” discarding the apartment information because it is in a format the software is not designed to 

standardize. 

After the address is standardized, the CODE-1 Plus® software 

determines if the standardized address is a valid USPS deliverable

address. Similar to the output of the physical location estimation (step 3), the output includes information that can be used 

to assess the precision of the “deliverability assessment.” For 

instance, the output will tell you if USPS recognizes the basic 

street address but does not recognize the apartment number.

Finally, in step 3, GSC attempts to estimate the physical location of the address using commercial software (GCP 5.2), a 

commercial base map (TomTom), and associated lookup tables. 

The important thing to note is that the GCP 5.2 software interpolates the spatial location based on street segment address ranges

(highest precision), ZIP+4 centroid (next highest precision), 

or ZIP Code centroid (lowest precision). These precision levels 

have been termed “high,” “medium,” and “low,” respectively.

2. Description of Process 

Used To Construct Public 

Housing Unit-Level 

Addresses

This section describes the process used to construct public 

housing unit-level addresses from the building entrance address 

and door number information in the existing IMS/PIC system 

and information extracted from HUD Form 50058 BLOB (or 

Binary Large Object) files, which are described in detail in 

subsection 2.3.

2.1 Determining What Constitutes 

a Usable Address

It is important to understand the relationship, and differences, 

between geocoding and address matching. Geocoding, as described in subsection 1.7, is the process of taking a raw address, 

standardizing it, conducting a deliverability assessment, and 

estimating where it is physically located on the landscape. 

Address matching is the process of taking two addresses and 

determining if they represent the same physical place. In an 

address-matching project, it is common to standardize 

addresses first and then implement text matching between 

address elements.1

When conducting geocoding or address matching, the user 

determines when an address should be considered “usable.” 

Recall from subsection 1.7 that the CODE-1 Plus® software 

determines whether an address is deliverable, and the GCP 5.2 

software estimates the spatial location of the address. Each of 

these processes comes with levels of precision. The two processes are entirely separate, relying on different data sources.

For some uses, such as mapping, it is likely sufficient for a 

standardized address to be present and to have a medium to 

1

 An alternative matching method is to use ZIP+6, which is often a unique 11-digit ZIP Code for each housing unit.
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high level of spatial precision while not meeting any tests of 

deliverability. By contrast, for address matching projects, it is 

often very important that a standardized address be present and 

deliverable, regardless of the spatial location precision.

An additional consideration for address matching projects is 

the uniqueness of the standardized address. For example, suppose a researcher is seeking to match public housing units with 

health survey responses using the address of the respondent. 

Further suppose the researcher has a health survey response 

from 123 Main St. Apt 1. When researchers match to the HUD 

public housing data, they find two public housing units sharing 

the same address. This finding may cause the researchers to 

discard the survey response because they could not determine 

which of the two public housing units responded to the survey. 

In fact, the HUD public housing data have many instances of 

two different units having the same address. 

For the remainder of this paper, a public housing unit-level address is considered usable if it is deliverable with high precision 

and a unique address among all public housing units. Appendix A 

describes the definition of “deliverable with high precision.” 

2.2 Initial Assessment of Address 

Usability

Before describing the process for constructing unit-level public 

housing addresses, it is useful to establish a baseline against 

which improvement can be measured. When the GSC geocodes 

addresses, they typically are using only the information available in the five core address fields: address line 1, address line 

2, city, state, and ZIP Code. GSC does not use any information 

from the optional door number field that exists in IMS/PIC. 

As mentioned in subsection 2.1, different users have different 

standards for declaring an address usable, and the standard 

adopted for assessment will depend on a user’s needs. Although 

the usable address standard chosen for this paper is “deliverable with high precision and unique,” baseline results are 

presented for address geocoding precision standards (table 7).

The baseline results for geocoding precision are consistent with 

previous expectations. Nearly 87 percent of addresses have 

high geocoding precision, meaning enough information was 

contained within the five address fields to estimate the location 

of the building entrance to a rooftop. This result suggests PHAs 

are generally doing an adequate, although not perfect, job of 

entering building entrance addresses.

Table 7. Baseline Results of Geocoding Precision and 

Address Matching Usability Using Typical GSC Process

Address Geocoding Precision Level Percent of

PH Addresses

High: “Rooftop” precision 86.5

Medium: ZIP+4 centroid 7.6

Low: ZIP Code centroid 5.8

Total 100

Address Matching Usability Level

Usable: Deliverable with high precision and unique 4.7

Not usable: Not deliverable with high precision 

and/or not unique

95.3

Total 100

GSC = Geocoding Service Center. PH = public housing.

The baseline results for address matching usability are far lower 

than previous expectations. Recall that 44 percent of public 

housing units have building entrance addresses that are actually 

unit-level addresses, simply because of the processes in place for 

recording building entrances. As such, if PHAs are recording 

building entrance addresses correctly, as many as 44 percent of 

units could be expected to have deliverable with high precision 

and unique unit-level addresses. The actual result was 4.7 percent, suggesting that PHAs are recording building entrance 

addresses that are not deliverable, per USPS standards.

2.3 Using HUD Form 50058 BLOB Files

Separately from the manual entry of building entrance addresses 

into the online IMS/PIC,2 HUD collects public housing tenant 

information, including unit-level addresses, on form HUD 

Form 50058. Address information on form HUD Form 50058 

is collected by PHAs within their respective record systems and 

electronically uploaded to HUD headquarters as raw text files, 

often referred to as “BLOB files.” Most of the HUD Form 50058 

BLOB information is parsed and stored in various tables in 

IMS/PIC. For public housing, however, the unit-level address 

information from HUD Form 50058 BLOB files is not currently 

parsed and stored in IMS/PIC. As such, the only building- and 

unit-level address information currently stored in IMS/PIC is 

the information entered by PHAs. It is worth noting that IMS/

PIC system was not designed to store every field parsed from 

the HUD Form 50058 BLOB files, including the address fields. 

It was designed based on program requirements in place during 

system development.

2

 In practice, each PHA has its own software that collects address information and uploads it to IMS/PIC.
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2.4 Process for Improving Unit-Level 

Addresses

This subsection describes the multistage process for constructing 

unit-level addresses. These processes were run on a September 

2013 quarterly extract of IMS/PIC. It is important to note that, 

beginning with stage 2, the procedures in each stage are applied 

to addresses deemed not usable after the previous stage. For 

instance, stage 2 processes are applied to any addresses deemed 

not usable after stage 1 processes were completed.

Stage 1

Stage 1 of the process for constructing unit-level addresses consisted of two parts. Part 1 included adding door numbers to the 

existing information in the first address field (address line 1). 

Part 1 also included a manual review of the text information in 

the door number field for a small sample of units, followed by 

development and application of code to repair common issues 

preventing the construction of a usable unit-level address.

Part 2 of stage 1 consisted of a manual review of the text information in address line 2 for a small sample of units, when 

present, followed by development and application of code to 

repair common issues preventing the construction of a usable 

unit-level address. As mentioned before, various PHAs enter 

addresses differently in the online IMS/PIC. As such, some 

information in the address line 2 field represented apartment 

numbers, some information represented the full address, and 

some information was erroneous. Where feasible, information 

in the address line 2 field was added to the address line 1 information to form a full address. 

Stage 2

Stage 2 of the process for constructing unit-level addresses consisted of extracting unit-level address information from HUD 

Form 50058 BLOB files. Each day, PHAs upload the HUD 

Form 50058 BLOB files to HUD. These daily BLOB uploads 

contain only records that have been updated since the previous 

upload (typically, the previous day). Given current public housing operating procedures, however, it is nearly a certainty that 

PHAs will have completed a new HUD Form 50058 sometime 

during the previous year for each household currently participating in public housing.

Section 5A of the HUD Form 50058 contains the unit address 

and apartment number. In effect, this source of address information is entirely separate from what is contained in IMS/PIC. 

As designed, however, IMS/PIC does not parse the HUD Form 

50058 BLOB unit address information and store it in a table.

Scripts were written to extract the address fields from the HUD 

Form 50058 BLOBs. The process was conducted only for the 

units for which stage 1 improvement efforts did not yield a 

usable address (about 17 percent of units).

Stage 3

Stage 3 of the process for constructing unit-level addresses consisted of manually inspecting, correcting, and testing building 

entrance addresses in public housing developments that contained 

a large number of nonusable addresses. The process can generally be described as—

1. Extract the building entrance addresses for a single public 

housing development with many nonusable addresses and 

combine it with the door number field to form a full address.

2. Visually inspect the addresses to determine why the addresses 

are not usable in their current form.

3. Use the current address information, including any additional 

information from HUD Form 50058 BLOB files in stage 2, to 

develop a proposed unit-level address.

4. Test the usability of the proposed unit-level address against 

the USPS ZIP Code Lookup application, the GSC Geocoder, 

Google Maps, and general web searches.

5. When a proposed unit-level address is found to be usable, 

create SAS code to apply the revision technique to all the 

unit-level addresses in the development.

The process was followed for 88 separate public housing developments across numerous states. In some cases, the revision 

process to construct the unit-level address was as simple as 

concatenating a few fields or removing erroneous information. 

In other cases, the revision process was complicated. What held 

true through the revision process was that if one address in the 

public housing development required a particular type of revision, virtually all the addresses required the same revision. 

Stage 4

Stage 4 of the process for constructing unit-level addresses consisted of a simple assumption and subsequent implementation 

of that assumption. The assumption was that a small fraction of 

building entrance addresses that, after three previous stages of 

improvement attempts, were still not deemed usable perhaps 

had been updated in the IMS/PIC with better addresses. The 

original building entrance addresses for this address construction 

project were derived from a September 2013 IMS/PIC extract. 

These original building entrance addresses then underwent the 
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previous three stages of development to turn them into usable 

unit-level addresses. It was hypothesized, however, that other 

building entrance address revisions (improvements) or additions of door numbers could have been entered into IMS/PIC 

by PHAs after September 30, 2013. If PHAs revised building 

entrance addresses or door numbers after September 30, 2013, 

these revisions should be present in a current IMS/PIC extract.

A short process was developed that included the following steps.

1. Determine which building entrance addresses were still not 

usable after stage 3.

2. For those building entrance addresses, extract the current 

IMS/PIC building entrance address information (where 

applicable) from a June 30 snapshot of PIC.

3. Evaluate the June 30 addresses to determine if they were 

usable. When usable, replace the September 30, 2013 address 

with the June 30, 2015 address.

Stage 5

Stage 5 of the process for constructing unit-level addresses was 

nearly identical to stage 3. The only major difference was that 

building entrance addresses (including door numbers) were 

evaluated on a PHA basis rather than a development basis. The 

move to PHA-based evaluation was undertaken because it was 

discovered after stage 4 that building entrance address entry issues (or door number entry issues) preventing the construction 

of usable unit-level addresses were often consistent at the PHA 

level, meaning that many or all of the public housing developments within the PHA shared the same address entry issue. 

The stage 5 process can generally be described as—

1. Extract the building entrance addresses and door numbers 

for a PHA with many nonusable addresses.

2. Visually inspect the building entrance addresses and door 

numbers to determine why they are not usable in their current form.

3. Use the current building entrance addresses and door numbers, including any additional information from BLOB files 

in stage 2, to develop a proposed unit-level address.

4. Test the usability of the proposed unit-level address against 

the USPS ZIP Code Lookup application, the GSC Geocoder, 

Google Maps, and general web searches.

5. When a proposed unit-level address is found to be usable, 

create SAS code to apply the revision technique to all the 

building entrance addresses and door numbers in the PHA.

The process was followed for 18 separate PHAs across numerous states. In some cases, the revision process to construct the 

unit-level address was as simple as concatenating a few fields 

or removing erroneous information. In other cases, the revision 

process was complicated.

3. Result of Address 

Construction Procedures 

and Conclusion

The final results of the unit-level address construction procedures

are presented in table 8. Stage 1 efforts dramatically improved 

Table 8. Final Results of Geocoding Precision and Address Matching Usability

Address Geocoding Precision Level Initial Percent of 

PH Addresses

Stage 1

(%)

Stage 2

(%)

Stage 3

(%)

Stage 4

(%)

Stage 5

(%)

High: “Rooftop” precision 86.5 91.5 92.8 92.9 93.0 92.9

Medium: ZIP+4 centroid 7.6 3.5 3.5 3.5 3.5 3.7

Low: ZIP Code centroida 5.8 5.0 3.7 3.6 3.5 3.4

Total 100 100 100 100 100 100

Address Matching Usability Level

Usable: Deliverable with high precision and unique 4.7 83.1 89.6 91.9 92.1 92.8

Not usable: Not deliverable with high precision and/or not unique 95.3 16.9 10.4 8.1 7.9 7.2

Total 100 100 100 100 100 100

PH = public housing.

a

 In stage 5, the percentage of unit-level addresses with high address geocoding precision actually went down by 0.1 percent. Although a curious result, it is easily 

explained. In stage 5, about 6,000 building entrance addresses were fixed. About 1,000 of these building entrance addresses had high address geocoding precision 

but actually were not a reflection of where the unit was located. It is possible the original address was an address of a main building. Regardless of the reason, after the 

building entrance address was fixed and verified as deliverable with high precision and unique, the resulting unit-level addresses within the building entrance had less 

address geocoding precision than the original address. In other words, the geocoding software could physically locate the original building entrance address, but the 

address was not where the unit was physically located.
Constructing Unit-Level Addresses in the 

Public and Indian Housing Information Center

2015 AHS Redesign Series 9

the number of usable unit-level addresses, and moderate gains 

were made in each subsequent stage. In addition to the large 

improvements in the number of usable unit-level addresses for 

address matching, small gains were made the in the geocoding 

precision level.

It is worth putting the results in the context of the effort necessary to achieve them. In subsection 1.5, it was hypothesized 

that unit-level addresses could be constructed from existing 

IMS/PIC information for as many as 98 percent of public housing units. Of course, this conclusion assumes that the building 

entrance address information currently in IMS/PIC and the 

supplemental apartment number information (door number) 

optionally entered into IMS/PIC by PHAs were correct.

The baseline assessment of address usability concluded that 

only 4.7 percent of addresses were deliverable with high 

precision and unique. This result, however, was based on the 

current GSC processes, which made no use of the supplemental 

apartment number information contained in IMS/PIC and 

which attempted to correct only a handful of systematic errors 

in address entry.

In stage 1, a major improvement occurred in the usability of 

unit-level address (from 4.7 to 83.1 percent). This dramatic 

result essentially was achieved by two steps. The first step was 

to use the supplemental apartment number information by 

adding it to the existing building-level address. The second step 

was to fix many systematic errors in the way building entrance 

addresses were entered into IMS/PIC. These two steps did not 

require a significant amount of manual inspection.

Stage 2 improved usability from 83.1 to 89.6 percent. This 

improvement was achieved by making use of the HUD Form 

50058 BLOB files, which are in effect a secondary source of 

unit-level address information. Much like stage 1, stage 2 did 

not require a significant amount of manual inspection.

Stages 3 and 5 consisted of a significant amount of manual 

inspection to repair development- and PHA-specific address 

entry errors to construct usable unit-level addresses. The net 

return on these two stages was 3.2 percent. The return on Stage 

4 was 0.2 percent.

Given the experiences with stages 3 and 5, it can safely be 

concluded that a large amount of manual effort would be 

required to construct additional unit-level addresses and move 

the needle from 92.8 percent to the hypothesized 98 percent.
Constructing Unit-Level Addresses in the 

Public and Indian Housing Information Center

2015 AHS Redesign Series 10

Appendix A. Defining What Is “Deliverable With High Precision”

Unit-level address matching between HUD public housing units 

and the American Housing Survey (AHS) or the American Community Survey is conducted using the U.S. Census Bureau’s 

Master Address File (MAF). The MAF is a master list of all residential addresses in the United States used by the Census Bureau 

for conducting its censuses and surveys. It is primarily based on 

data supplied by the U.S. Postal Service (USPS) but is augmented 

with canvassing operations conducted by the Census Bureau and 

feedback from local jurisdictions. In the MAF, each unit-level 

address is assigned a unique number called the MAFID. The 

Census Bureau takes the standardized HUD public housing unit 

addresses and matches them to the MAF such that each public 

housing unit receives a unique number. The process is repeated 

for the AHS. When the process is complete, the match between 

HUD public housing units and the AHS is a simple process of 

matching on MAFID.

The Geocoding Service Center’s commercial geocoding software 

includes a Delivery Point Validation (DPV) determination. Generally speaking, this determination reflects if USPS delivers mail 

to the address. To be more specific, the determining takes the 

values described in table A-1.

On first glance, it is tempting to conclude that Y is the only DPV 

code that truly means deliverable. HUD, however, conducted 

an analysis of how often HUD public housing units uniquely 

matched with the MAF and how the match rates varied by DPV 

code value. The results showed that public housing units with 

DPV codes Y, N, and D nearly always produced unique matches 

with the MAF, but DPV code S did not. Although it is somewhat 

difficult to explain this result for DPV codes N and D, it is 

nonetheless an important result. 

Using the results of this analysis, HUD made the determination 

that public housing unit-level addresses with DPV codes Y, N, 

and D would be classified as “deliverable with high precision.”

Table A-1. DPV Codes

DPV 

Code Meaning

Y Confirmed; entire address was DPV confirmed as deliverable.

N Not confirmed; address could not be DPV confirmed as deliverable.

S Confirmed by dropping secondary information (apartment, suite, 

etc.).

D Confirmed, but missing secondary information (apartment, suite, 

etc.).

DPV = Delivery Point Validation.