Topic 9: Data Exploration

Question 1

Introduce/ Review the 6 elements of spatial analysis

Answer 1

1. Measurement: direct measurements from the locations and/or attributes of geographic entities
2. Queries: questions posed to the database that also do not involve changes to the database
3. Descriptive Summaries: summary statistics and other quantitative metrics characterize geographic attributes and entities
4. Transformations: spatial operations that transform geographic data into new information
5. Design & Optimization problems: methods designed to solve practical problems of design routing, or optimal location
6. Prediction and inference: advanced spatial models that use geographic information to estimate patterns or infer the processes behind geographic phenomenon

Question 2

Discuss GIS operations for: Measurement

Answer 2

• Simplest method: Pythagorean or Euclidean (Assumption that points are used on a flat plane, can only be used with a PCS
• Great Circle Distance (geodesic distance) measured on a spherical model of the Earth
• Remember that all measurements in GIS are an approximation, due to the representation of real-world entities and distortions in the projection
• Tends to underestimate the distance
• Area Measurement: of digital polygons in a GIS (comprised of polylines) is relatively simple and reliable

Question 3

Discussion GIS operations for Queries (non-spatial and spatial database queries)

Answer 3

• Spatial queries operate “Select by location” (found under the selection menu) (eg., select features that: intersect, that are within distance of, that are completely contained by, that contain, etc.)
• Non-spatial (attribute) queries interrogate the attribute tables using structured query language (SQL) syntax

Question 4

Discuss GIS operations for Descriptive statistics (non-spatial and spatial summaries)

Answer 4

• Descriptive statistics provide a concise, quantitative summary of the characteristics of a variable or data set
• In addition, descriptive statistics can also be used for creating improved designs

Question 5

Spatial statistics terms

Answer 5

Central tendency: Numerical = Mean, median, (mode); Spatial = Mean centre or median centre
Absolute Variability: Numerical = Standard Deviation; Spatial = Standard Distance
Relative Variability: Numerical = Coefficient of variation; Spatial = Relative Distance

Question 6

Applications of Spatial Median

Answer 6

The spatial median defines the point of minimum aggregate travel, it is often used for determining the ‘optimal’ location for facility location in urban/ economic geography

Question 7

Relative Spatial Variability: Relative Distance

Answer 7

• Unfortunately like with the coefficient of variation, you can’t just divide the standard distance of the coordinates by the mean distance to get a relative measure of variability
• So have to divide by a measure of regional magnitude: the radius of a circle with the same area as the region being analyzed