(THIS IS AN EXAMPLE OF DOCUMENTATION FOR STATE BLOCK
GROUP BOUNDARY COVERAGE)
METADATA FOR MABG
(Substitute any 2-letter state abbreviation for MA.)
/* Identification Information */
Data_Set_Identity: MABG -- Census block groups for states from 1990 TIGER/Line files
Identification_Code: N/A
Theme_Keyword: Census block groups
Thematic_Accuracy: See Attribute Descriptions
Thematic_Accuracy_Explanation: See Attribute Descriptions
Logical_Consistency: Polygon topology present
Completeness: See Data_Set_Description
Data_Set_Citation:
Hitt, K.J., 1994, Digital map file of 1990 Census block group boundaries
for the United States processed from Bureau of the Census 1990 TIGER/Line
files: Washington, D.C., The Bureau (producer and distributor), 1:100K
scale, ARC/INFO format.
Native_Data_Set_Environment: UNIX
Use_Restrictions: See Data_Set_Description
Access_Restrictions: Not reviewed
Security_Classification: UNCLASSIFIED
/* Spatial Reference */
Native_Data_Set_Structure: ARC/INFO COVER
Horizontal_Coordinate_System: Planar
Map_Projection_Name: ALBERS
Map_Projection_Coordinate Units: METERS
Horizontal_Datum_Name: NAD27
Ellipsoid_Name: CLARKE1866
Vertical_Datum_Name: NGVD29
Longitude_of_Central_Meridian: -96 0 0.000
Latitude_of_Projection_Origin: 23 0 0.000
Latitude_of_First_Standard_Parallel: 29 30 0.000
Latitude_of_Second_Standard_Parallel: 45 30 0.000
False_Easting: 0.00000
False_Northing: 0.00000
X-Shift: 0.0000000000
Y-Shift: 0.0000000000
Point/Vector_Object_Information:
Number of points: 12192
Number of lines: 25485
Number of line segments: 378528
Number of polygons: 12193
Point_Object_Information:
Number of control points: 56
Horizontal_Positional_Accuracy: N/A
Horizontal_Positional_Accuracy_Explanation: N/A
Vertical_Positional_Accuracy: N/A
Vertical_Positional_Accuracy_Explanation: N/A
West_Bounding_Coordinate: -73.6247
East_Bounding_Coordinate: -69.3767
North_Bounding_Coordinate: 42.5975
South_Bounding_Coordinate: 41.7306
Data_Set_G-Polygon_Outer_G-Ring: N/A
Data_Set_G-Polygon_Exclusion_G-Ring: N/A
Geographic_Keyword_Name: United States
Geographic_Keyword_Type: Location
/* Status Information */
Data_Set_Status:
Not reviewed
Release_Date: N/A
Maintenance_and_Update_Frequency: N/A
/* Metadata Reference Section */
Metadata_Date: 950906.153657
Metadata_Review_Date: N/A
Metadata_Future_Review_Date: N/A
Metadata_Contact: kjhitt
/* Source Information */
Source_Identity:
Hitt, K.J., 1994, Digital map file of 1990 Census block group boundaries
for the United States processed from Bureau of the Census 1990 TIGER/Line
files: Washington, D.C., The Bureau (producer and distributor), 1:100K
scale, ARC/INFO format.
/* Processing History Information */
/* Per Process Step */
Process_Description: MAPJOIN MABGGEO POLYS ALL
Process_Date: 06/07/1994 (MDY)
Process_Time: 12:48
Process_Description: PROJECT COVER MABGGEO MABG /SRV1/TEMP/KJH/EPABG/ALB.PRJ
Process_Date: 06/07/1994 (MDY)
Process_Time: 12:53
Process_Description: BUILD MABG POLY
Process_Date: 06/07/1994 (MDY)
Process_Time: 13:28
Process_Description: TOLERANCE MABG
Process_Date: 08/22/1994 (MDY)
Process_Time: 17:18
Process_Description: ARCEDIT /SRV1/TEMP/KJH/EPABG/MA25/MABG
Process_Date: 09/02/1994 (MDY)
Process_Time: 11:50
Process_Description: BUILD MABG POLY
Process_Date: 09/06/1994 (MDY)
Process_Time: 9:08
Process_Description: DOCUMENT MABG CREATE KJHITT
Process_Date: 09/07/1994 (MDY)
Process_Time: 14:36
Process_Description: COPY MABG /SRV3/NAWQA/KJH/BG/MABG
Process_Date: 10/13/1994 (MDY)
Process_Time: 16:30
Process_Description: DOCUMENT MABG UPDATE KJHITT
Process_Date: 10/24/1994 (MDY)
Process_Time: 10:12
Process_Description: EXPORT COVER MABG /VAR/FTP/PUB/KJH/MABG.E00
Process_Date: 12/19/1994 (MDY)
Process_Time: 16:49
Process_Description: KJHITT TOLERANCE MABG LIST
Process_Date: 07/28/1995 (MDY)
Process_Time: 15:04
Process_Description: KJHITT DOCUMENT MABG DELETE KJHITT
Process_Date: 09/06/1995 (MDY)
Process_Time: 15:36
Process_Description: KJHITT DOCUMENT MABG COPY /SRV3/NAWQA/KJH/BG/AKBG KJHITT
Process_Date: 09/06/1995 (MDY)
Process_Time: 15:37
Process_Description: KJHITT EXPORT COVER MABG /SRV1/TEMP/KJH/BG/MABG.E00
Process_Date: 09/06/1995 (MDY)
Process_Time: 18:32
/* Distribution Information */
Distribution_Contact: Kerie Hitt, USGS-WRD-NAWQA
Distribution_Liability: N/A
Transfer_Options: N/A
Transfer_Instructions: N/A
Fees: N/A
Turnaround: N/A
/* Contact Information */
Contact_Organization: USGS-WRD-NAWQA
Contact_Person: Kerie Hitt
Contact_Position: N/A
Contact_Mailing Address: N/A
Contact_Physical Location: N/A
Contact_Voice_Telephone: N/A
Contact_Facsimile_Telephone: N/A
Contact_Electronic_Mail_Address: N/A
Contact_Instructions: email kjhitt@usgs.gov or phone 703/648-6854
/* Entity/Attribute Information */
Data_Base_Identity: MABG
Partition_Identity: N/A
Entity_Type_label: MABG.PAT
---------------------------------
Entity_Type_Definition: BLOCK GROUP POLYGONS FOR STATES
Entity_Type_Definition_Source: 1990 TIGER FILES
Number_of_Attributes_in_Entity: 12
Attribute_Label: -
Attribute_Definition: BLOCK GROUP POLYGONS FOR STATES
Attribute_Definition_Source: 1990 TIGER FILES
EA_Domain_Values: -
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: AREA
Attribute_Definition: Area of poly in square coverage units
Attribute_Definition_Source: Computed
EA_Domain_Values: Positive real numbers
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: PERIMETER
Attribute_Definition: Perimeter of polygon in coverage units
Attribute_Definition_Source: Computed
EA_Domain_Values: Positive real numbers
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: MABG#
Attribute_Definition: Internal feature number
Attribute_Definition_Source: Computed
EA_Domain_Values: Sequential unique positive integer
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: MABG-ID
Attribute_Definition: User-assigned feature number
Attribute_Definition_Source: User-defined
EA_Domain_Values: Integer
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: STATE
Attribute_Definition: 2-digit state FIPS code
Attribute_Definition_Source: TIGER files
EA_Domain_Values: 01 - 56
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: COUNTY
Attribute_Definition: 3-digit county FIPS code
Attribute_Definition_Source: TIGER files
EA_Domain_Values: -998
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: CTBNA
Attribute_Definition: Census tract/Block numbering area 6-digit code
Attribute_Definition_Source: TIGER files
EA_Domain_Values: 0001 - 9499.9 (CTs) and 9501 to 9980.99 (BNAs)
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: BG
Attribute_Definition: Block group id number within CTBNA
Attribute_Definition_Source: TIGER files
EA_Domain_Values: -8
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: LAND/WATER
Attribute_Definition: Flag for land or water block group
Attribute_Definition_Source: TIGER files
EA_Domain_Values: L and W
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: BGI
Attribute_Definition: Block group unique identification number
Attribute_Definition_Source: TIGER files
EA_Domain_Values:
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Attribute_Label: STCNTRBG
Attribute_Definition: Block group unique identification number
Attribute_Definition_Source: TIGER files
EA_Domain_Values:
EA_Units_of_Measure: N/A
EA_Measurement_Precision: N/A
EA_Beginning_Date: N/A
EA_Ending_Date: N/A
EA_Accuracy: N/A
EA_Accuracy_Explanation: N/A
EA_Measurement_Frequency: N/A
Data_Set_Description:
1. Abstract
This is a polygon coverage of the 1990 Census TIGER/Line block groups
organized by state. Approximately 230,000 block groups exist in the
United States.
Descriptors:
United States
Population
Census
2. Applications that use this data
This coverage could be used for any GIS application requiring the
Census block group as the basic geographic unit. The block groups
are the geographic areas used to extract the population points from
the P.L. 94-171 data base for the coverage USPOP90 that is in the
Distributed Spatial Data Library.
2.1 Intended use of data
The NAWQA nutrients national synthesis intends to use population
density by block group to derive urban land use for water-quality
studies.
2.2 Limitations of data
The TIGER files have no shorelines. Coastal areas have their
boundaries extended approximately 3 miles into the ocean. Areas
bounding the Great Lakes and other large inland waterbodies have their
boundaries extended proportionally into the waterbody.
The coverage contains no arc attributes, only polygon attributes.
3. Attribute discussion
The state block group coverage .pat files contain the following
attributes, where XX is the 2-letter state postal abbrevation:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC
1 AREA 8 18 F 5
9 PERIMETER 8 18 F 5
17 MABG# 4 5 B -
21 MABG-ID 4 5 B -
25 STATE 2 2 C -
27 COUNTY 3 3 C -
30 CTBNA 6 6 C -
36 BG 1 1 C -
37 LAND/WATER 1 1 C -
38 BGI 12 12 C -
** REDEFINED ITEMS **
25 STCNTRBG 12 12 C -
STATE------state FIPS code
COUNTY-----county FIPS code
CTBNA------Census tract (CT)/Block numbering area (BNA)
BG---------block group number within CTBNA
LAND/WATER-flag for whether the block group is land or water
L = land
W = water
BGI--------block group identifier, consisting of:
BGI 0 1
columns 123456789012
xx - state FIPS
xxx - county FIPS
xxxxxx - Census tract/block numbering area (CTBNA)
x - Block group within CTBNA
xxxxxxxxxxxx - Unique block group identifier
Census block groups are the next to smallest geographic area in the
Bureau of the Census hierarchy of geographic presentation, which
is:
United States
Region
Division
State
County
County subdivision
Census tract/Block numbering area (BNA)
Block group
Block
Census blocks are small areas bounded on all sides by visible
features such as streets, roads, streams, and railroad tracks, and by
invisible boundaries such as city, town, township, and county limits,
property lines, and short, imaginary extensions of streets and roads.
Tabulation blocks, used in census data products, are in most cases
the same as collection blocks, used in the census enumeration. In
some cases, collection blocks have been "split" into two or more
parts required for data tabulations. Tabulation blocks do not
cross the boundaries of counties, county subdivisions, places,
census tracts or block numbering areas, American Indian and Alaska
Native areas, congressional districts, voting districts, urban or
rural areas, or urbanized areas. The 1990 census is the first for
which the entire United States and its possessions are
block-numbered.
Blocks are numbered uniquely within each census tract or BNA. A
block is identified by a three-digit number, sometimes with a
single alphabetical suffix. Block numbers with suffixes generally
represent collection blocks that were "split" in order to identify
separate geographic entities that divide the original block. For
example, when a city limit runs through data collection block 101,
the data for the portion inside the city is tabulated in block
101A and the portion outside, in block 101B. A block number with
the suffix "Z" represents a "crews-of-vessels" entity for which
the Census Bureau tabulates data, but that does not represent a
true geographic area; such a block is shown on census maps
associated with an anchor symbol and a census tract or block
numbering area with a .99 suffix.
A block group is a cluster of blocks having the same first digit
of the 3-digit identifying numbers in a census tract/BNA. In
population data tabulations, a geographic block group may be
split. Therefore, when linked with the point population and
housing coverage (USPOP90), SOME OF THE BLOCK GROUPS CONTAIN MORE
THAN ONE POPULATION POINT. Block groups do not cross census tract
or block numbering area boundaries.
Census tracts are small, relatively permanent statistical
subdivisions of a county. They are identified by a four-digit
basic number and may have a two-digit suffix. Census tract numbers
range from 0001 to 9499.9 and are unique within a county. The
suffix .99 identifies a census tract that was populated entirely by
persons aboard one or more ships.
Block numbering areas (BNAs) are small statistical subdivisions of
a county for areas where census tracts are not established. They
are identified by a four-digit basic number and may have a
two-digit suffix. BNA numbers range from 9501 to 9980.99 and are
unique within a county. The suffix .99 identifies a census tract
that was populated entirely by persons aboard one or more ships.
Suffixes in the range of .80 through .98 usually identify census
tracts or BNAs that were revised or created during the 1990 census.
Some of these revisions may have resulted in census tracts or BNAs
that have extremely small land area and may have little or no
population or housing.
Census tracts and BNAs do not cross county boundaries.
4. Procedures used to create or automate data
The block group boundaries are from the 1990 Census Bureau TIGER/
Line files. The TIGER/Line files were converted into ARC/INFO by
the Environmental Protection Agency's National Geographic Information
System Program using ARC/INFO aml programs developed with USGS.
EPA provided USGS with county block group coverages in geographic
coordinates. The county coverages for each state were joined into
the state coverage, which was projected to albers.
The general processing steps for creating the block group
coverages for all of the counties in a state are shown below.
(Details about the amls can be obtained from Steve Denowski,
USGS-WRD, phone 608/238-9333, extension 160, or Dave Wolf, EPA,
phone 703/235-5592.) The ssccc means the FIPS code for a
particular county, where ss represents the state component and ccc
represents the county component:
1. Project the geographic coordinates of the TIGER line file into
albers equal area and build the coverage.
2. Create a join file with the RECNUM and CFCC items in
it. (These items are taken from the tl_ssccc.acode file for the
coverage.)
3. Sort the join file on the RECNUM.
4. Merge the join file with the tl_ssccc.aat using the RECNUM as
joinitem.
5. Dissolve the tl_ssccc coverage by the TRACTBLK item with the
POLY option (not the NET option)
6. Add the item 'CENSUS' to the dissolved coverage called
tl_ssccctb.
7. Move TRACTBLK to CENSUS in the tl_ssccctb coverage.
8. Redefine the first 7 characters of CENSUS as BG.
9. Add a new item called 'BGI' and calculate BGI = BG.
10. Dissolve the tl_ssccctb coverage by BGI using the POLY option.
11. Add a new item called 'FIPS' to the resulting coverage
tl_sscccbg and calculate FIPS = ssccc.
The 12-digit block group identifier BGI is calculated equal to the
STCNTBG.
5. Revisions made to data (revision number, date, description)
Sept 5, 1995. BGI altered from integer type item to character item to
get around integer limitation in ARC.
6. Reviews applied to data (review type, date, person, description)
The coverage has not been reviewed formally.
7. Related spatial and tabular data sets and programs
The 1990 population data by block group is located in the
Distributed Spatial Data Library in the layer called USPOP90.
(The block group identifier can be derived from the fields in the
CENSUS_ID. The items STATE, COUNTY, CTBNA, and BG must be
recombined in that order into a 12-digit code for block group that
matches the 12-digit BGI in the block group coverage.)
8. References cited
Bureau of the Census, 1991a, TIGER/Line Census Files, 1990 (machine-
readable data files): Washington, D.C., The Bureau (producer and
distributor).
Bureau of the Census, 1991b, TIGER/Line Census Files, 1990 technical
documentation: Washington, D.C., The Bureau, 63 p.
Hitt, K.J., 1992, Digital map file of 1990 population and housing
data for the conterminous United States processed from Bureau of
the Census, 1991, Census of population and housing, 1990: Public
Law 94-171 data (United States) (machine-readable data files):
Washington, D.C., The Bureau (producer and distributor), 1:2M
scale, ARC/INFO format.
9. Notes