Week 9: Point Pattern Analysis

Question 1

How do we work out if there is a higher probability of points occurring in one area compared to another?

Answer 1

Carrying out quadrat analysis

Question 2

How do we determine a random distribution using quadrat analysis?

Answer 2

If the average number of points per cell is roughly equal to the variance of the number of points per cell.

Question 3

How do we determine a clustered distribution using quadrat analysis?

Answer 3

If there is a large amount of variability.

Question 4

List some limitations of Ripley’s K(d).

Answer 4

• Dependent on study boundary area
• Circles go outside study area
• Each point has a unit value, there’s no magnitude or quantity

Question 5

What is nearest neighbour analysis?

Answer 5

Measures the distance of each points to its nearest neighbour, determines the mean distances between neighbours and compares the mean distance to what would have been expected in a random distribution.

Question 6

What are 3 ways of defining distance?

Answer 6

• Direct (standard)
• Indirect (linear)
• Based on a network

Question 7

Why is Kernel Density Estimation (KDE) useful?

Answer 7

• Generalises data over larger regions
• Good method to show estimation
• Provides a risk surface more than an actual picture of what is occurring.

Question 8

How does KDE work?

Answer 8

• Every point has a density estimate, and when you overlay a grid on top of a map, you transfer those density estimates on top of the grid.
• Measures the distance between each grid cell centerpoint and each incident data point and determines the cell weight for that point

Question 9

List 3 factors that the weight of each cell depends on.

Answer 9

• Distance fro the grid cell centerpoint to the incident data point
• Size of the radius around each incident data point
• Method of interpolation

Question 10

What is bandwidth?

Answer 10

Refers to the size of the cone of the kernel and is specified by the user.

Question 11

What does a bell curve shaped bandwidth represent?

Answer 11

• peaks and declines rapidly with no defined radius
• Continues across entire grid

Question 12

What does a uniform (flat) distribution bandwidth represent?

Answer 12

• All points in radius equal
• Represented by cylinder