Queries and 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 dataset (2 options) enables boolean algebraic calculations to create an index value based on multiple datasets?
Raster Datasets
What are the two main types of raster data?
What types of data are presented in each?
Discrete Raster: categorical/nominal data
ex: land use codes, soil types
Continuous Raster:
variable quantities over area
elevation, weather, etc.
What is map positional accuracy?
Positional Accuracy: a measure of the likelihood that features on a map are actually in the locations specified on the surface of the earth.
What name is given to raster data where x, y, and z coordinates are defined?
Voxcells
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 map unit is an indicator of an unprojected coordinate system in a map document?
Decimal Degrees
What are text characters stored as in a vector data set?
text = string 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 mathematical operations is conducted for a boolean raster where the values of one layer intersect another?
Multiplication (*)
True or False: queries can be conducted on joined tables.
TRUE!
Which operational tool (found when right-clicking on an attribute in a table) is used to determine the mean, mode, sum, & standard deviation of a given attribute?
Summary Statistics
Name three advantages or disadvantages of vector data model compared to raster.
Advantages Raster:
Good for complex analysis (e.g. map algebra)
Efficient for overlays
Data structure common for imagery
Advantages Vector:
Compact data structure
Efficient for encoding topology
True representation of shape
Disadvantages Raster:
Large datasets
No topology
Maps less "realistic“
(“blocky”)
Disadvantages Vector:
Complex 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
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
Name one open source GIS tool.
Q-GIS
Grass
Google Earth
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 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/classificicaton is 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 precip.
---
1. unique value
2. graduated color (choropleth)
3. standard deviation
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.
and, or and xor are commutative boolean 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 does the symbol signify in the image below? how is it fixed?
Broken data link: right click on layer > data> define data source
Which tool is 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.
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 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..