Flashcards in Human/ Physical GIS and Census Data Deck (59):
What does TIGER stand for?
What do TIGER files provide?
1. census geography polygons and linear and point feature data
2. to allow mapping the 1990 through 2010 censuses and placing them in context.
What is the objective of TIGER?
Objective is to map the census for each decade since 1990. Provides a wide range of scales of geographic aggregation following the census itself.
What levels is TIGER data available at?
Available at several levels from national – state – county with different internal identifiers to tie to the census enumeration units
What scale is TIGER best for?
Data are spatially accurate to 1:100,000 scale (NMAS of 167’), so good for moderate to smaller scale representations. Can be argued though that the census enumeration units are really thematic data bases - not really reference oriented to begin with. Accuracy also applies to features though!
How are feature types in the TIGER shapefiles coded?
Feature types in the Shapefiles are coded by the Master Address File / TIGER Feature Class Codes (MTFCC) which are made up of a letter and 4 digit number.
Feature data are all found in the “All Lines” shapefile at the county level. Some state level data are also available in the feature sets.
National and State TIGER files have the data units aggregated from _______ units to __________, and some for the entire US.
Is the scale still the same?
What are enumeration units downloaded at?
These files have the data units aggregated from county units up to states and some for the entire US.
All are still the same scale (1:100,000) so the detail levels are high for these larger units.
State or national level since 2011.
What are TIGER features and what are they included for?
What are the 7 TIGER features?
Tiger features are included for analytical purposes, and because many of the census unit geography edges use these features. There are a number of types (not all will appear in every county):
Physical Landmarks – mountain peaks, quarries (C)
Hydrology (H) – streams, ponds etc.
Human Landmarks – apartment, campground (K)
Linear Features – pipelines, power lines (L)
Railroads (R) – main line tracks
Roads and Highways (S) – coded by quality
What is Census geography?
The Census collects data from individual people and releases data about those people in aggregates of variable sizes.
A knowledge of the spatial units of data available is very helpful in research with GIS. As units get smaller, with fewer people in them, fewer variables are disclosed.
How do block, block groups, and census tracts relate to each other?
Census tracts are in block groups, which are in blocks.
Look at slide 16 for illustration (it'll make it easier to visualize)
What is are blocks?
Smallest units of data tabulation
Cover the entire nation
Do not cross census tracts or counties
Generally bounded by visible features and legal boundaries
Size: average about 100 people
Mcty: 3,560 blocks
What is the official definition for blocks? How many blocks are delineated for Census 2000? How have blocks been renumbered?
A block is defined as an area bounded on all sides by visible and/or invisible features shown on a map prepared by the U.S. Census Bureau. A block is the smallest geographic entity for which the Census Bureau tabulates decennial census data.
There are about 8,200,000 blocks delineated for Census 2000.
There has been a complete renumbering of blocks across the U.S. One other major change is that the numbering has gone from a three-digit system to a four-digit system. Water bodies were also assigned block numbers in Census 2000 for the first time.
What are block groups?
Groups of blocks sharing the same first digit
Smallest areas for which sample data (ACS) are made available
Size: optimally 1,500 people, range between 300 to 3,000
Mcty: 58 block groups
What is the official definition for block groups?
Block groups are the ________ entity for which the US Census Bureau tabulates sample data from decinnial census.m
A statistical subdivision of a census tract (or, prior to Census 2000, a block numbering area), a block group consists of a cluster of census blocks having the same first digit of their identifying numbers within that tract.
For example, for Census 2000, BG 3 within a census tract includes all blocks numbered from 3000 to 3999. (A few BGs consist of a single block.) BGs generally contain between 300 and 3,000 people, with an optimum size of 1,500 people.
What are census tracts?
Groups of Block Groups.
Relatively homogenous population characteristics
65,000 Census tracts across U.S.
Size: optimally 4,000 people, range between 1,000 and 8,000
Mcty: 16 tracts
What is the official definition for census tracts?
Census tracts are small, relatively permanent statistical subdivisions of a county or a statistically equivalent entity. Designed to be relatively homogeneous units with respect to population characteristics, economic status, and living conditions at the time they are established, census tracts generally contain between 1,000 and 8,000 people, with an optimum size of 4,000 people. Census tract boundaries are delineated with the intention of being stable over many decades, so they generally follow relatively permanent visible features. However, they may follow governmental unit boundaries and other invisible features in some instances; the boundary of a state or county is always a census tract boundary.
Census tracts are usually identified by a six-digit number composed of a four-digit basic number and a two-digit numeric suffix; for example, 8001.07. This suffix (.07) indicates that the original tract, tract 8001, was split possibly into seven pieces as a result of population growth. In some maps the census tract may be represented by a single digit number - in those cases the three leading zeroes were omitted for simplification. However, all census tracts have 6 digits (first four and the last two after the decimal).
In 1990 and previous censuses, the Census Bureau created tract-like geographic units, called Block Numbering Areas or BNAs, outside of metropolitan areas. BNAs were discontinued for Census 2000; instead, one or more census tracts were identified for every county and statistically equivalent entity.
Census tracts are usually delineated for data presentation purposes by a local group of census data users or the geographic staff of a regional census center in accordance with U.S. Census Bureau guidelines.
What are county subdivisions?
In many states these are local political units such as townships. In others they are census derived.
Do NOT have to follow minimum or maximum population guidelines, nor fit hierarchically with other census geography levels (eg. Tracts shown)
What is the official definition of county subdivisions?
A minor civil division (MCD) is the the primary governmental or administrative division of a county or statistically equivalent entity in many states and statistically equivalent entities. A minor civil division is created to govern or administer an area rather than a specific population.(ex. Town, Township, District) The U.S. Census Bureau recognizes minor civil divisions in 28 states, the District of Columbia, Puerto Rico, and the Island Areas.
A census county division (CCD) is a statistical subdivision of a county, delineated by the U.S. Census Bureau in cooperation with state and local government officials for data presentation purposes. A census county division usually represents one or more communities, trading centers or, in some instances, major land uses. The Census Bureau has established census county divisions in states that do not have minor civil divisions suitable for data presentation.
Minor civil divisions and census county divisions together cover the entire country and provide a standard level of geography below the county. Minor civil divisions are more common in the East, while census county divisions are more common in the West.
What are places?
Incorporated Places – towns and cities
Census Designated Places – “locally agreed upon” places and unincorporated “towns”
Note that these are not contiguous and do not fit in the hierarchy of blocks, block groups, and tracts.
Mcty: 10 places
What is the official definition of places?
There are two kinds of places in Census Bureau terminology: incorporated places and Census Designated Places (CDPs).
A place is a concentration of population legally bounded as an incorporated place. A CDP is delineated for statistical purposes as a census designated place (in Puerto Rico, a comunidad or zona urbana). These are created for the purpose of presenting census data for an area with a concentration of population, housing, and commercial structures that is identifiable by name, but is not within an incorporated place. For Census 2000, for the first time, CDPs did not need to meet a minimum population threshold to qualify for tabulation of census data.
As you can see in this map taken from the American FactFinder, the boundaries of places - either incorporated or CDPs - do NOT necessarily correspond to census tracts, block groups or MCDs.
Speaker note: CDP boundaries, which usually coincide with visible features or the boundary of an adjacent incorporated place or other legal entity boundary, have no legal status, nor do these places have officials elected to serve traditional municipal functions. CDPs usually are delineated in cooperation with state, Puerto Rico, Island Area, local, and tribal officials based on U.S. Census Bureau guidelines.
What are counties?
Counties in 48 States
Parishes in Louisiana
Cities and Boroughs in Alaska
Independent Cities in 4 States
National File – does not include accurate coastlines
What is the official definition of counties?
Counties are the primary subdivision of most states. A number of geographic entities are not legally designated as a county, but are recognized by the U.S. Census Bureau as equivalent to a county for data presentation purposes.
What are congressional districts?
National Files only.
What is the key for census geography?
Key is to balance geographic resolution versus the needs for privacy.
-Too small a unit makes the data to close to the individuals who provided it
-Too large a unit does not give a good picture of variations in the data.
-Some data are more “private” than others: Age, Gender, Race, Income, House Value
For key fields within the census, unique names exist __________.
Within each level, but not across levels.
-County codes are unique within states
-Tract codes are unique within counties
-Block codes are unique within tracts
To maintain unique names across units, census geography that is hierarchical in nature (Blocks-Block Groups-Tracts-Counties-States) uses a __________
Concatenation of name levels to build unique names outside of their own level (up to nationally). Block Groups are defined by the first digit of each block name.
Block names are not ____________
Block names are not unique except within census tracts – thus neither are block group names.
The left most digit of the block id is the _________.
The left most digit of the block id is the block group. It too is unique only within a tract.
While the TIGER shapefiles all have the codes needed to use with the census, they do not include___________
any census demographic data at all
How is demographic data obtained?
Demographic Data are all obtained in tabular (list) formats and then joined into the Featureclass tables via relational data structures. (next)
Specific tables of Data are collected separately from the US Bureau of the Census website with a variety of tools
The 2010 Census shows _________ and the U.S. and the American Community Survey shows _________.
The number of people who live in the U.S.
How people live.
How do we obtain data for the extract desired data tables today?
Today we can use the American Factfinder tool (http://factfinder2.census.gov) to extract desired data tables with codes that can be related to the TIGER datasets we looked at last time.
Prior to the 2010 census, the decennial census sent out two types of data gathering surveys every ______ years. What are these twp types of data survey?
The long form (40 pp. in 2000) and the short form (6 pp. in 2000). A sample of the population received the long form that requested a great deal more information from respondents. Long form data were released in summary file 3 in 2000
After 2000 the long form was replaced by a smaller sample survey done _______. What was this called?
The American Community Survey (14pp)
-Data are aggregated over a period of ACS into 1, 3 and 5 year data. Longer period is given in smaller units (down to BGs).
-BGs are for 2010 if the survey period ended in 2010 or later.
Data down to tracts is also available from _______.
American Factfinder system
Enumeration units run from _______.
US down to block groups (same as the 2000 SF3.)
BGs are available only by Excel Macro downloads, not on American Factfinder
The ACS provides data on how we live. Unlike the census which makes its counts every ten years (it does produce estimates every year for larger units), the ACS gives us a new picture of how people live every year based on running 1, 2, or 5 year averages. Of the following, all census units are available from the ACS except:
C) Block groups
What does the USGS National Map provide?
The National Map provides the nation with access to basic geographic information describing the landscape of the United States and its territories. It has many uses ranging from recreation to scientific analysis to emergency response. The National Map is easily accessible for display on the Web, printed products, and as downloadable GIS data. The geographic information available from The National Map consists of terrain elevations, aerial imagery, hydrography, transportation, boundaries, structures, geographic names, and land cover.
Why is the national map viewer useful?
Useful for making a custom map using USGS products. You can order products or create your own mapping for your purposes all on-line.
Download raster data on elevation, land cover.
Download vector data from this site for hydrology, transportation etc.
What data is available on the national map viewer/
5. Geographic names
6. Map Indices
9. Land cover
What are DRGs?
DRG – Digital Raster Graphics – scanned and georeferenced topographic maps, both current and historical.
What are structures?
Structures -name, function, location, and other characteristics of selected manmade facilities. Types of structures collected are largely determined by the needs of disaster planning and emergency response organizations
What is transportation?
roads, airports, railroads, and other features associated with the transport of people or commerce.
What are boundaries?
government boundaries (political units)
What are geographic names?
Geographic Names – GNIS data on place names and feature names (streams, mountains etc.)
What are map indices?
USGS topographic map boundaries for 1x2 degrees, 1x1 degree, 1 x 0.5 degrees, 30 x 60 minutes, 15 x 15 minutes, 7.5 x 7.5 minutes (these are basically just quadrangles.
What is hydrography?
high resolution topologic stream data (1:24,000)
What are contours?
vector elevation data threaded through 1/3 second NED data
What is land cover?
NLCD data derived from LandSat data (1992, 2001, 2006, 2011 – underway)
What is elevation?
NED data - raster elevations
What is orthoimagery?
"picture" data from aerial photography at 6" to 1 meter resolution
What is the National Elevation Dataset (NED)?
These used to be called Digital Elevation Models and still are by many.
Today, data originally collected by individual quadrangle topographic maps have been seamlessly tied together into the National Map data server at several scales.
As of August 2012, all raster data are also placed in the national map viewer for download making it a one-stop download site.
What are the specifications for NED datasets?
1” – spacing of 1 arc second ( 30 meters)
1/3” – spacing of 1/3 arc second ( 10 meters)
1/9” – spacing of 1/9 arc second ( 3.3 meters)
Available throughout the US, at 1/3”, 1/9” is nearly complete
NAD83 Geographic coordinates
Data are available in pre-tiled sections that form rectangular areas around your selected region
County NED data are downloaded by county name using the NED Tile tool as of 2012.
With three resolutions available (1”, 1/3”, and 1/9”), the NED dataset is a very popular dataset. Given that we can get elevation data at about 3.3 meters (1/9”) why might so many users still prefer the 1” NED data?
A)They are used to them
B)The higher resolution data are much larger datasets
C)The NLCD layer is 30 meters and the1” match that.
D)The 1” data are more accurate thanthe finer resolution products.
The 1” data are more accurate thanthe finer resolution products
What is the National Land Cover Database?
Landcover in multiple classes based on LandSAT 5 & 7 satellite data
30 – meter resolution classified images
1992, 2001, 2006, and 2011 data are available for time comparisons.
What data is available from the USDA Geospatial Data Gateway that isn't available in the National Map?
1) TIGER – blocks, block groups, and tracts – also some census data tables
2) Climate – precipitation – vector polygons and raster
3) Climate – temperature – vector polygons
4) Easements – Conservation land polygons
5) Geology – general – national scale
6) Hydrologic Units – watershed polygons
7) Soils – STATSGO and SSURGO data for digital soil surveys.
What is STATSGO2 data?
STATSGO2 data are at a nominal scale of 1:250,000 with a minimum mapping unit of 2,500 acres. These are very generalized data, but good for working in large areas.
Available as ESRI shapefiles
NAD83 Geographic coordinates
Selected by state
What is SSURGO data?
SSURGO data are at a nominal scale of 1:12,000 or 1:24,000 with a minimum mapping unit of 1 to 10 acres, good for detailed soil work
Available as ESRI shapefiles
NAD83 geographic, UTM or State Plane coordinates available.
Selected by soil survey area