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Guide to Use of CDBG Block Level Data

4/28/ 2 10:09: QKW_RITE: GatherM3Ms: Data ID 3189

Guide to the Use of CDBG Block Level Eligibility Materials

(this report was created 11/18/14 22:25)

Background and Purposes of the Project (this report was created 11/18/14 22:25)

The Division of Housing & Neighborhood Development, part of the Department of Human Services of Polk County, has initiated this analysis of data based upon the 1990 Census of Population and Housing. (this report was created 11/18/14 22:25)

The purpose of the project is to identify areas eligible for CDBG expenditures, and to identify these areas at the block level. Block level analysis is needed because census block groups are too large to permit identification of some small but eligible and deserving neighborhoods. (this report was created 11/18/14 22:25)

Data from the 1990 census dealing with counting people, housing units, families, and race, age, and type for each is available from what is called the 100% count, or "STF1". This data is from the brief questionaire which was mailed to nearly all homes in the U.S. in April, 1990. This data is available on CD-ROM for census block groups. Data from the 100% count (STF1), is available at the block level on tape and an extract of it is available on a CD-ROM. (this report was created 11/18/14 22:25)

Data on income is available from a sample of approximately 17% of people and is called "sample data", or "STF3". This data is available at the census block group level but not at the block level. (this report was created 11/18/14 22:25)

The following table shows the value of block level analysis for Polk County. (this report was created 11/18/14 22:25)

The Number of Geographic Areas by Census Summary Level

Polk County

Summary Level County Code Summary Level Code # of Areas # Areas with Pop. Total Population
County 12105 50 1 1 405382
County subdivision 12105 60 6 6 405382
Place 12105 70 48 46 405382
Census tract/BNA 12105 80 189 172 405382
Block group 12105 90 490 447 405382
Block 12105 100 7253 7171 405382
Total 72630 450 7987 7843 2,432,292

Methodology for Estimating Income at the Block Level (this report was created 11/18/14 22:25)

This methodology used involves shifting the curves of income distribution (available at the block group level) so that they reasonably reflect the probable incomes of families and unrelated individuals in each of the blocks that comprise the block group. Various steps of callibration and quality control analysis then force all numbers to aggregate back correctly to block group data and report on the probable range of error. These techniques are not innovative; they have been in use by statisticians and data modellers for several decades. Techniques include decile distribution analysis and procedures for handling missing data so that suppression of data in some areas by the Census Bureau for reasons of confidentiality will not impede analysis. The various steps in this process are described more fully below. (this report was created 11/18/14 22:25)

Some Caveats Helpful in Using Materials from this Study (this report was created 11/18/14 22:25)

The following comments are offered to aid in interpreting the work undertaken in this study. (this report was created 11/18/14 22:25)

"Census blocks" are often far larger than the area circumscribed by four city streets. Sparsely populated areas, especially, may have very large "blocks". (this report was created 11/18/14 22:25)

Block numbers are placed at the center of the block area in maps produced in this study, not at the centroid. In some cases, as in an "L" shaped block, the block number can be outside the perimeter of the block. (this report was created 11/18/14 22:25)

The 1990 Tiger files are used for mapping eligibility data to be sure that all boundaries are the same as those used for the 1990 Census of Population and Housing. (this report was created 11/18/14 22:25)

County-wide data is referred to as "summary level 50" data. Similarly, block level data is referred to as "summary level 100". The following is a list of the summary levels that are widely used. This study uses summary levels 50, 60, 70, 80, 90 and 100 so that the greatest amount of detail available from the census is used. Often, when tract data or block group data are used, they are from summary levels 140 and 150; data levels which may cross the boundaries between two "places" or towns. This CDBG study respects the boundaries of all cities, towns and other "places". (this report was created 11/18/14 22:25)

Definitions of Summary Level Codes

All Census Areas of the U.S.

1. 10 United States     1C/3C*
2. 20 Region     1C/3C
3. 30 Division     1C/3C
4. 40 State (totals) 1A/3A 1C/3C*
5. 50 County (totals) 1A/3A 1C/3C
6. 60 County subdivision (MCD/CCD) (totals) 1A/3A  
7. 61 County subdivision (>10000)   1C/3C
8. 62 County subdivision (<10000) (MSA/CMSA)   1C/3C
9. 70 Place (parts) 1A/3A  
10. 80 Census tract/BNA (parts) 1A/3A  
11. 90 Block group (parts)    
12. 91 Block group (parts) 1A/3A  
13. 100 Block      
14. 140 Census tract/BNA (totals) 1A/3A  
15. 150 Block group (totals) 1A/3A  
16. 155 County (parts) 1A/3A  
17. 160 Place (totals) 1A/3A  
18. 161 Place (>10000)   1C/3C
19. 170 Consolidated city (totals) 1A/3A 1C/3C

The following "county subdivision codes", assigned by the Bureau of the Census, are used in this study. (this report was created 11/18/14 22:25)

90117 Bartow division 91209 Frostproof division 91404 Haines City division 91833 Lakeland division 91859 Lake Wales division 93718 Winter Haven-Auburndale division

The following "county place codes (FIPS)", assigned by the Bureau of the Census, are used in this study. (this report was created 11/18/14 22:25)

2550 Auburndale city (pt.) 2900 Babson Park CDP 3675 Bartow city 13775 Combee Settlement CDP 15515 Crooked Lake Park CDP 15725 Crystal Lake CDP 16050 Cypress Gardens CDP 16450 Davenport city 18550 Dundee town 18875 Eagle Lake city 24100 Fort Meade city 24900 Frostproof city 25125 Fussels Corner CDP 25875 Gibsonia CDP 28400 Haines City city (pt.) 30225 Highland City CDP 30325 Highland Park village 30700 Hillcrest Heights town 34000 Inwood CDP 35300 Jan Phyl Village CDP 35950 Kathleen CDP 37525 Lake Alfred city 37975 Lake Hamilton town 38250 Lakeland city (pt.) 38262 Lakeland Highlands CDP 38950 Lake Wales city 41400 Loughman CDP 43925 Medulla CDP 47200 Mulberry city 57950 Polk City town (pt.) 74775 Wahneta CDP 75475 Waverly CDP (pt.) 77862 Willow Oak CDP (pt.) 78200 Winston CDP 78275 Winter Haven city (pt.) 99999 Remainder of division

The following codes for "Project Areas" are used in this effort. (this report was created 11/18/14 22:25)

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