Queries & Joins
Describe the terms of a data relationship when a simple join occurs. Give three main factors.
A simple join is a temporary data relationship.
Cardinality = one to one or many to one
Common fields between tables must be the same data type
Which map unit is an indicator of an unprojected coordinate system in a map document?
Decimal degrees
What data format stores text characters stored as attributes in a vector data set?
Text = String values/alphanumeric values
(as opposed to integers, floating points, etc.)
What type(s) of map is(are) best suitable for ratio data depicted as polygons?
Choropleth maps
What is the difference between positional accuracy and temporal accuracy?
Positional accuracy refers to whether or not locations on a map are as they exist in the real world.
Temporal accuracy considers whether the time period for a data set is valid..
How do the two main (Vector) data query tools differ?
Select by Attributes: Generates a subset of data based on shared characteristics of a single attribute.
Select by Location: generates a subset based on proximity or other map placement characteristics.
Which operational tool is used to determine the mean, mode, sum, & standard deviation of a given attribute within a vector dataset?
Summary statistics
Name three advantages or disadvantages of vector data model compared to raster data.
Advantages: Vector
•Compact data structure
•Efficient for encoding topology
•True representation of shape
Disadvantages: Vector
•Complex data structure
•Overlay operations difficult
•May require more preprocessing (e.g. cleaning topology)
What are basic topological rules? Give one example.
Topology: rules of spatial relationships in vector data
Basic Rules
- Adjacent polygons share coincident boundaries
- Lines should always meet (and not dangle)
-Intersections only occur where nodes exist
- Nodes exist only where three or more lines intersect
- Lines do not intersect and form loops
- No duplicate/copies of feature data
What is logical consistency for map data?
The location of an object, its position/shape/appearance are correct and consistent across data formats, usages, etc. in comparison with the actual object.
True or false: Queries can be conducted on joined tables.
TRUE! Data queries can be conducted from any attribute table, joined or stand-alone.
What must be consistent in order for field calculations to incorporate data from other attributes?
Data types must be consistent (numeric: Double, integer, etc.)
Give one example of displaying vector data as values, but NOT numbers
Graduated symbol (point, line)
Graduated color (polygon/choropleth)
Which type of symbology/classificaton is most appropriate for the following data?
Household income per county
Names of water bodies
Highest and lowest annual precipitation
---
1. Unique value
2. graduated color (choropleth)
3. standard deviation
Link data type with appropriate map type
2. Household income per county
1. Names of water bodies
3. Highest and lowest annual precipitation
---
1. Unique value
2. graduated color (choropleth)
3. standard deviation
What name is given to a geographical datum that combines both a spheroid and a geographical reference point meant to minimize map distortion for objects in the USA, Canada and Mexico?
North American Datum (NAD)
Explain the difference between simple, summarized & spatial joins.
Simple join: one to one/many to one
Summarized: overcomes rule of joining violations, totals values of one to many/many to many
Spatial: Considers proximity/containment
What is the symbol in GIS software that signifies a broken data link? How is it fixed?
Red exclamation point in layer window/table of contents: Right click on layer > data> Define Data Source; select appropriate data source in your directory.
Which data query tool can be used to determine the number of cities within a given distance of an airport?
Select by Location
Why do we normalize data? Under what conditions would it be appropriate to do so?
Normalization helps overcome data distortion due to MAUP (Modifiable Areal Unit Problem).
Large areas or large populations can create MAUP effects in choropleth maps. By dividing values by the total population or area, the map values more accurately represent a comparative analysis display.
What term refers to a digital file that stores both spatial data as well as information on how to display it in a given map project?
Layer/Layer File
AND, OR and XOR are commutative operations.
What does that mean?
Values are transversal: A AND B is equal to B AND A.
Order of operations does not matter for values A and B.
Operations applied right-to-left can also be applied left-to-right.
What is Positional Accuracy? Give an example where software might adversely affect this condition.
Positional Accuracy: A measure of the likelihood that features on a map are actually in the locations specified on the surface of the earth.
Ex 1: Improper coordinate systems = area/distance errors
Ex2: Forgetting to recalculate area/distance fields after clip/erase if a user-generated attribute.
Which resolution of the options below would ensure the greatest likelihood of snapping tolerance for coincident boundaries? What tradeoffs may result?
- 500m
- 1000m
- 1500m
1500m likely ensures the greatest potential snapping tolerance for shared/coincident boundaries.
However, map accuracy and precision are likely diminished as a result.
Why would a map contain less-than precise or accurate locations of spatial data? When might this be appropriate?
To protect the condition of cultural/historic artifacts, secure facilities, etc.
Archaeological maps, Military maps, private data maps, etc.
What spatial data elements provide rules for what content can be included in an attribute table to help avoid errors in data entry and encourage consistency? Give an example of one.
Domains/Domain Types:
Range Domains: min/max values
Coded Domains: a list of possible values to select