US Census Geocoding - trillium_discovery - trillium_quality - 17.2

The US Postal Matcher has an option to enrich address information with latitude and longitude coordinates, derived from the US Census Tables. This process is called geocoding. US Census directories are optional components that can be purchased with the US Postal Matcher.

Coordinate Accuracy Levels

Latitude and longitude coordinates are returned at the following levels of accuracy. See Frequently Asked Questions for answers to some of the common questions about the US Postal Matcher Census Geocoding.

True Rooftop (Interpolated Rooftop+)

True Rooftop coordinates are linked to a specific complete address using the house number, street name, city name and any other relevant address components. The coordinate information are taken directly from the supplier's data. This is the most precise form of latitude / longitude coordinates.

Codes returned from a match to the data describe the location of the coordinates. Possible returns are:

• Parcel
• Structure
• Street Frontage
• Driveway Offset
• Front door

All other fields that are described in the #US_Census_Geocoding__drop1 section are also returned.

Interpolated Rooftop Coordinates

Interpolated rooftop coordinates are linked to a specific complete address using the house number, street name, city name and any other relevant address components. They are calculated by using information taken from the supplier's data.

The mapping data supplier describes streets by using street segments. A street may consist of one or more segments. Each segment generally describes a straight section of the street. As a result, they vary in length depending on how straight the street is overall.

The definition of a street segment includes:

• Start and end coordinates
• The range of house numbers that the segment covers
• The side of the on which the street house numbers fall

Example. In the following example, the highlighted street has three segments, with the ranges of house numbers and the side of the street they occur as shown.

The following process describes how the street segment definition is calculated:

Trillium calculates the coordinates for any house number on the street using the start and end points of the segment that contain the house number. Using the position of the house number within the segment’s range, Trillium calculates how far from the start point the house number lies. (This assumes that all houses within the segment occupy the same amount of space.) This calculation produces a point on the street (the red icon on the map). Trillium offsets the position perpendicular to the line of the street segment on the correct side of the street to generate a realistic position for the building (the blue icon on the map). The size of the offset is determined by classification of the street, which is taken from the supplier’s data and indicates the type of street; for example, highway, major road, and so on.

Interpolated Rooftop Geographic Codes

The Interpolated Rooftop geocode level returns the following geographic codes:

• FIPS State Code - FIPS is an abbreviation for Federal Information Processing Standards. This field contains a numeric code for the identification of the states, the District of Columbia and the outlying areas of the United States, and associated areas.
• FIPS County Code - FIPS is an abbreviation for Federal Information Processing Standards. This field contains a numeric code for counties and equivalent entities of the United States, its possessions, and associated areas. These are used in conjunction with the state code as the county numbers are unique per state. Three digit, standard, non-zero, odd number between 001 - 999 that depicts a primary political subdivision of a state.
• Census Tract Code - According to the US Census Bureau, census tracts are small, relatively permanent statistical subdivisions of a county. Census tracts are delineated for most metropolitan areas (MA's) and other densely populated counties by local census statistical area committees following Census Bureau guidelines. The values that are appended to a record are based on the 2000 Census. Six states (California, Connecticut, Delaware, Hawaii, New Jersey, and Rhode Island) and the District of Columbia are covered entirely by census tracts.
• Census tracts usually have between 1,500 and 8,000 persons and, when first delineated, are designed to be homogeneous with respect to population characteristics, economic status, and living conditions. Census tracts do not cross county boundaries. The spatial size of census tracts varies widely depending on the density of settlement.
• Census tract boundaries are delineated with the intention of being maintained over a long time so that statistical comparisons can be made from census to census. However, physical changes in street patterns caused by highway construction, new development, etc., may require occasional revisions; census tracts occasionally are split due to large population growth, or combined as a result of substantial population decline.
• Interpolated Rooftop+ assigns latitude/longitude based on a specific address using the house number, street name, city and any other relevant address components.
• Census Block Code - The smallest Census Bureau geography entity. It is generally in an area bounded by streets, stream and the boundaries of legal and statistical entities.
• Census Place Code - FIPS code assigned to places (including independent cities).
• Census Place Name - Corresponding name for the returned Place Code.
• Census Sub Minor Civil Division (SMCD) - A further subdivision of a MCD; specifically, a sub-barrio in Puerto Rico.
• Core Based Statistical Area (CBSA) - According to the US Census Bureau, Metropolitan and Micropolitan Statistical Areas-collectively are called Core Based Statistical Areas (CBSAs). It is a unit containing a substantial population nucleus (urban core) together with adjacent community having a high degree of economic and social integration with that core. The urban core of a metropolitan statistical area has a population of 50,000 or more, the urban core of a micropolitan statistical area has a population between 10,000 and 50,000.
• CBSA Name - Corresponding name for the returned CBSA code.
• County Name - Corresponding name for the returned County Code.
• Latitude - The angular distance, up to 180 degrees North or South of the equator, which is measured in degrees to six decimal places. The latitude is based on the coordinates of the endpoints of a street. Latitude for a specific house number is interpolated based on the house number ranges for the street. If the house number is not within the house number range, the latitude of the beginning of the street is returned.
• Longitude - The angular distance, up to 180 degrees East or West of the prime meridian, in Greenwich, England, measured in degrees up to six decimal places. The longitude is based on the coordinates of the endpoints of a street. Longitude for a specific house number is interpolated based on the house number ranges for the street. If the house number is not within the house number range, the longitude of the beginning of the street is returned.
• Minor Civil Division (MCD/CCD) - According to the US Census Bureau, the 2 major types of county subdivisions are Minor Civil Divisions (MCD) and Census County Divisions (CCD). A state can have either MCDs or their statistical equivalents or CCDs, but a state cannot contain both. MCDs are the primary subcounty governmental/administrative unit; they have legal boundaries and names as well as governmental functions or administrative purposes specified by state law. The most familiar types of MCDs are towns and townships. The Census Bureau also establishes UTs (unorganized territories) that it treats as statistically equivalent to an MCD in certain states for parts of counties not in an MCD. The US Census Bureau recognizes MCDs or MCD equivalents in 28 states and DC. Census county Divisions are statistical entities established cooperatively by the US Census Bureau and state/local government officials in the 21 states where MCDs do not exist.

Note: The following fields are no longer updated by the source provider since the fields are no longer supplied by the Census Bureau: MSA, MSA Name, NECMA, NECMA Name.

Note: As of v15.5, the Centroid products no longer contain MCD data and all the MCD attributes are filled with zeros.

• Metropolitan Statistical Area (MSA) - The US Census Bureau states that metropolitan and micropolitan statistical areas consist of one or more counties.
• MSA Name - Corresponding name for the returned MSA Code.
• NECMA (NECTA) Code - According to the US Census Bureau, the New England city and town areas (NECTAs) are defined using the same criteria as metropolitan and micropolitan statistical areas and are identified as either metropolitan or micropolitan, based, respectively, on the presence of either an urbanized area of 50,000 or more population or an urban cluster of at least 10,000 but less than 50,000 population.
• NECMA (NECTA) Name - Corresponding name for the returned NECMA (NECTA) Code.

Zip+4/Zip5/City Centroid Geographic Codes

The US Zip+4/Zip5/City Centroid Census geocode level returns the following geographic codes:

• FIPS State Code - FIPS is an abbreviation for Federal Information Processing Standards. This field contains a numeric code for the identification of the states, the District of Columbia and the outlying areas of the United States, and associated areas.
• FIPS County Code - FIPS is an abbreviation for Federal Information Processing Standards. This field contains a numeric code for counties and equivalent entities of the United States, its possessions, and associated areas. These are used in conjunction with the state code as the county numbers are unique per state. Three digit, standard, non-zero, odd number between 001 - 999 that depicts a primary political subdivision of a state.
• Census Tract Code - According to the US Census Bureau, census tracts are small, relatively permanent statistical subdivisions of a county. Census tracts are delineated for most metropolitan areas (MA's) and other densely populated counties by local census statistical area committees following Census Bureau guidelines. The values that are appended to a record are based on the 2000 Census. Six states (California, Connecticut, Delaware, Hawaii, New Jersey, and Rhode Island) and the District of Columbia are covered entirely by census tracts.

Census tracts usually have between 1,500 and 8,000 persons and, when first delineated, are designed to be homogeneous with respect to population characteristics, economic status, and living conditions. Census tracts do not cross county boundaries. The spatial size of census tracts varies widely depending on the density of settlement.

Census tract boundaries are delineated with the intention of being maintained over a long time so that statistical comparisons can be made from census to census. However, physical changes in street patterns caused by highway construction, new development, etc., may require occasional revisions; census tracts occasionally are split due to large population growth, or combined as a result of substantial population decline.

• Census Block Group Code - According to the US Census Bureau, block groups are clusters of blocks within the same census tract having the same first digit of their 4-digit census block number. For example, blocks 3001, 3002, 3003,..., 3999 in census tract 1210.02 belong to BG 3.

A BG usually covers a contiguous area. Each census tract contains at least one BG and BGs are uniquely numbered within census tract. Within the standard census geographic hierarchy BGs never cross county or census tract boundaries, but may cross the boundaries of county subdivisions, places, urbanized areas, voting districts, congressional districts, and American Indian/Alaska Native areas/Hawaiian home lands.

• Latitude - The angular distance, up to 180 degrees North or South of the equator, which is measured in degrees to six decimal places. Zip+4/Zip5 Centroid provides a latitude value for an address based on the center point (centroid) of the Zip+4 or Zip5. If there is no match to the Zip+4 then a match will be attempted at the Zip5 level. If the City Centroid option is selected, the latitude of the center point (centroid) of the city is returned.
• Longitude - The angular distance, up to 180 degrees East or West of the prime meridian, in Greenwich, England, measured in degrees up to six decimal places. Zip+4/Zip5 Centroid provides a longitude value for an address based on the center point (centroid) of the Zip+4 or Zip5. If there is no match to the Zip+4 then a match will be attempted at the Zip5 level. If the City Centroid option is selected, the longitude of the center point (centroid) of the city is returned.