u.s. census data & tiger/line files
DESCRIPTION
U.S. Census Data & TIGER/Line Files. Census Bureau: Charged with the Constitutional responsibility of carrying out the decennial census Census of Population and Housing Very large mapping component involved in undertaking a national census! Census demographic/socioeconomic data: - PowerPoint PPT PresentationTRANSCRIPT
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U.S. Census Data & TIGER/Line Files
Census Bureau: Charged with the Constitutional responsibility of carrying out the decennial
census Census of Population and Housing
Very large mapping component involved in undertaking a national census! Census demographic/socioeconomic data:
Demographic, economic, & social data about persons & households Aggregated by census enumeration units: e.g. block, block group, tract,
county, metropolitan area, etc… TIGER/Line files:
The “geography” of the census Topogically Integrated Geographic Encoding & Referencing e.g., polygons for enumeration units, streets & landmarks
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TIGER/Line files - background 1967 - New Haven Census Use Study
test digital data structures for storing census data by geographic areas test processes for creating computerized Census maps had topology!!
1970s - Census DIME files expansion of New Haven study into production version data coverage: U.S. urban areas important component of 1980 decennial Census
1980s - development of TIGER/Line files incorporated DIME files for urban areas (DIME updated in 1981 & 1985) incorporated nationwide 1:100,000 USGS DLG data additional information from local officials & Census fieldwork
1990s – TIGER in use used for 1990 Census TIGER updated nearly yearly after 1990 from variety of sources 1998-1999: major update & prep for 2000 Census
2000 - latest Census 2nd use of TIGER for Census data being released now
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TIGER/Line Files
TIGER designed to: support pre-census functions in preparation for
Census of Population and Housing support census-taking efforts evaluate success of the Census provide geographic framework for analysis
Nominal scale: 1:100,000 Data "layers":
Enumeration units blocks, block groups, tracts/block numbering areas,
counties, cities/MA, etc. multiple hierarchies
Voting districts used for Congressional redistricting
Supporting geography roads/streets/highways basic hydrography point & area landmarks etc...
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TIGER Area (polygon) & Landmark Data Point and poly landmarks
Census geography (tracts, blocks, etc.) used for reporting Census data ID linkage from polygons
in TIGER/Line data to Census attribute data
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TIGER Line and Address Data Linear features...
Form polygon boundaries Roads
attributes include basic road type, address ranges
also hydro features, etc.
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Link to Census Data Census attribute data - Summary Tape File (STF) data
files
Link to Census geographic entities in TIGER/Line files using unique Census geography IDs
Lets us merge a tremendously rich souce of detailed socioeconomic data (Census) with a comprehensive geography for the entire country…
Orange County, NC block groups w/ median income data (darker green = higher income)
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hierarchical tabulation systems, e.g.:
USA
Region
Division
State
County
Tract
Block Group
Block
2000 Census tallies for entire US:
65,443 tracts
208,790 block groups
8,205,582 blocks
for NC:
1,563 tracts
5,271 block groups
232,403 blocks
Census Geographic Hierarchy
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TIGER Address Data
address ranges: street address numbers at beginning and ending of arc/line in database allows address geocoding
match data with address to a spatial location using an interpolated estimate
data use implication: explosion of analysis and data integration capabilities! extremely large (and growing) amount of data tied to addresses
problem: incomplete address range data, esp. in rural areas
--why? some areas simply have incomplete data (very large data collection task) PO rural routes (though this is changing due to E-911 systems)
Census Bureau steadily improving rural address data private street/address data providers enhance address range data
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Relational Database Structure
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Relational DBMS
Data stored as tuples (tup-el), conceptualized as tables
Table – data about a class of objects Two-dimensional list (array) Rows = objects Columns = object states (properties, attributes)
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Row = object
Column = property
Table = Object Class
Object Classes withGeometry called Feature Classes
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Relation Rules
Only one value in each cell (intersection of row and column)
All values in a column are about the same subject
Each row is unique No significance in column sequence No significance in row sequence
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Joined Table
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Relational Join
Fundamental query operation Occurs because
Normalization Data created/maintained by different users, but integration
needed for queries Table joins use common keys (column values) Table (attribute) join concept has been extended to
geographic case
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Normalization
Process of converting tables to conform to relational rules
Split tables into new tables that can be joined at query time The relational join
Several levels of normalization Forms: 1NF, 2NF, 3NF, etc.
Normalization creates many expensive joins De-normalization is OK for performance optimization
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Spatial Relations
Equals – same geometries Disjoint – geometries share common point Intersects – geometries intersect Touches – geometries intersect at common boundary Crosses – geometries overlap Within– geometry within Contains – geometry completely contains Overlaps – geometries of same dimension overlap Relate – intersection between interior, boundary or exterior
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Two Possible Relations
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Point Quadtree
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Region Quadtree