Ch 2: Data Flashcards
spatial
where an object is located or an event has occurred
temporal
when the location and attributes were accurate (when collected)
attribute
what characteristics the object or event has
example of spatial charactertistic
Spatial characteristics of data, like location of state boundaries(or address, coordinates) are needed to put the data on a map
example of temporal characteristic
Temporal characteristics refer to how data represent a “snapshot” of what things were like at the time the data were collected, such as census data from 2000
example of attribute characteristic
Attribute characteristics describe the nature of a location (population, income, etc)
2 main methods of spatial data collection
ground surveying and remote sensing
ground surveying
involves a person or mechanism that observes or interacts with people or the environ. in a particular place
remote sensing
refers to collecting data from afar, often by taking pics from a plane or satellite
ground surveying in depth
Ground surveying conducted through individual/mechanism interacting with a particular place
Can include a person collecting locational data with handset that works with GPS, constellation of satellites that beam signals to earth where they can be used to determine position
Surveys involve talking to people or traveling to different locations to gather info
Another kind of ground surveying occurs at weather stations that measure temp and other climatological info at a given location
what process is ground surveying similar to?
geo coding
what is geocoding
data with locational elements (address, zipcode) are matched to known ground coordinates
land surveying
-determines location
Use tools to determine precise positions of locations by triangulating from the position of known locations
Land surveyors helped map out many countries, working outward from known to unknown locations
gps in depth
GPS are constellations of satellites that orbit Earth
Satellites transmit signals to earth’s surface to indicate their position in space and a precise time signal
Device equipped with GPS receiver can interpret these signals and find device’s location earth
what type of surveying is gps considered
Considered ground surveying since it’s the handset or GPS unit that’s determining position from satellite signals
drawbacks of gps
signals can be blocked by solid objects and getting a strong signal can be hard, limited number of satellites orbiting Earth, depending on quality of handset GPS coordinates could be inaccurate
Space segment system based on velocity
control segment
ground stations that monitor and maintain the satellite vehicles
user segment
receivers detecting and interpreting signals (use signals to calculate position)
geo coding
process of attaching a geographic location to address information
Most use some form of database of addresses whose locations are precisely known
surveys
gather attribute info about individuals, households, businesses or area
Data gathered can be linked to location on a map
Census collects data on all members of a population
sensors
used to measure a wide array of human and environmental facts
Location determined by GPS, ground surveying or geocoding
remote sensing
-collected at a distance from object they are studying
Some sensors collect imagery with cameras
Detect different non visible parts of the electromagnetic spectrum, infrared (heat)
Used for monitoring changes in the environment over large areas (deforestation)
metadata
data about data that lets you assess how well the data can work with other data
example of metadata
Such as the content, source, lineage, methods, developer, coordinate systems, extent, structure, spatial accuracy and the responsible organization for spatial data
census data
Primary source of social data used by government, nonprofits and businesses
background to census
US census conducted every 10 years and collects info about the race, age and housing situation of the population
Purpose is to determine the number of seats each state will have in the US House of Representatives, legislative branch of government
Censuses also determine how billions of dollars in federal funding is distributed for many purposes (education, health care, environmental protection, transportation, etc)
Data from census and ACS (American Community Survey) are collected from each household, but in order to preserve privacy and to make data easier to use, Census Bureau combines the data to larger geographic areas
Canadian census → critical for allocation of government resources and conducted every 10 years
Census data used to redraw ridings used to elect people and process based on: pop. equity, community identity, historical patterns and maintaining a manageable geographic site
limitations of census data
Primary challenge is accuracy and undercounting (homeless are missed in the count)
Plenty of topics aren’t covered, quantity and wording of questions asked changed over time, data not always available for all places or geographic areas
key concepts to consider when choosing data to analyze a specific problem
Resolution, accuracy and interoperability with respect to 3 elements of spatial data (location, attributes, time)
resolution
Describes the breadth or specificity of data you are examining
3 main types: spatial, attribute and temporal
Higher resolution corresponds with smaller areas over which data are collected, narrower distinctions between categories, or shorter times between data collection
spatial resolution
measure of the smallest object that can be resolved by sensor
attribution resolution
deals with the degree to which distinctions are made between categories
-Data split into many categories provide more detailed distinctions and higher attribute resolution
temporal resolution
frequency with which data is collected
accuracy
Describes how well data on a map aligns with objects in the world
spatial accuracy
how well an object’s location on the map matches its location in the world
example of spatial accuracy
boundaries between countries drawn incorrectly, GPS points offset if signal blocked, etc
attribute accuracy
-whether characteristics reported about an object are true about that object in the world
-Inaccuracies show up in survey data if participants don’t respond, misunderstand or provide false information; or when estimating values for small area based on small number of responses
temporal accuracy
concerned with whether details about an object are up-to-date with respect to changes in the world
Accurate at time of collection but because of changes to social and physical landscape → becomes inaccurate (e.g. printed reference map)
interoperability
Describes how well two different datasets work with each other
spatial interoperability
how well do spatial units match up
E.g. zip codes and census tracts are spatial units for which data are frequently collected but their boundaries are rarely the same
Zip Code level data and census tract level data have poor interoperability as they don’t show characteristics for same group of people
attribute interoperability
how well do the categories of 2 datasets match?
E.g. in 2010 census, people could pick from between 15 racial categories with option of selecting multiple categories
By comparison, in the 1850 census, individuals were divided into only three racial categories: “white,” “black,” or “mulatto.”
These two datasets have poor attribute interoperability because they have very different attribute resolution and do not have matching categories.
temporal interoperability
how well do reported times match up?
Of most concern if making an argument about what things are like at one point in time but your data are not from same point in time
E.g. if you are working at a nonprofit that’s trying to compare number of children ages 0-5 to the number and location of early childhood centers in an area, most accurate count of children is from the 2010 census, but your organization has information about childhood centers collected in 2015
These two datasets have poor temporal interoperability because no children who were 0-5 at the time of the census would still be in that age bracket in 2015.
It would be hard to determine whether childhood centers are appropriately located based on this data.
trilateration
Need 3 reference points and exact location is where all 3 intersect
Gives coordinates (3 points)
In space, reference points are satellites
metadata
data about data that describes factors such as the content, source, lineage, methods, developer, coordinate systems, extent, structure, spatial accuracy and the responsible organization for spatial data
geocoding
process of attaching a geographic location to some sort of address information
-it takes an address and transforms it into a pair of coordinates that can be plotted on a map
