W5

Question 1

What does point distance analysis

Answer 1

Determines the distances from input point features to all points in the near features within a specified search radius

Question 2

What does nearest neighbourhood analysis do?

Answer 2

Calculates the distance and additional proximity information between the input features and the closet feature in another layer or feature class

Question 3

What do vector format buffers do?

Answer 3

creates polygons around input features to a specified distance

Question 4

Do projections matter for buffers?

Answer 4

Yes, geodesic buffers actually account for the actual shape of the earth
- calculates distance on a curved surface vs flat surface (cartesian plane)

Question 5

What is a Thiessan polygon

Answer 5

Thiessen polygons partition the space based on proximity to a set of point locations.
- they are created by dividing a geographic area into polygons such that each polygon encompasses all the points within its boundary that are closer to its defining point (site) than to any other defining point.

Question 6

How do local functions work?

Answer 6

only use data at a single location to calculate an output value
- uses all logical operators
- can use all functions of map algebra
- can calculate cell statistics

Question 7

How do focal (neighbourhood) functions work?

Answer 7

Uses data from a set of neighbourhood cells (kernels)
- relates a cell to its neighbours
- Explicitly make use of spatial proximity within a local neighbourhood
- used to determine values in a new output grid

Question 8

How do zonal functions work?

Answer 8

Uses data in regions or groups
- operates on regions to which the cells belong
- zones are group of grid cells that share the same value
- these zones are typically defined on a separate grid

Question 9

How global functions work?

Answer 9

use all data from a raster layer
- Output is cells in each location that have a function of all cell values in the input layer

Question 10

What raster function is used to calculate distance?

Answer 10

• global, this is because their operations and calculations take the entire extent of the raster into account
• projection issues are important especially when calculating absolute distances

Question 11

What does the straight line distance function do?

Answer 11

measures the straight line (euclidean) distance from each cell to the closet source (aka the object of interest)
- if a source grid is used the distances are calculated from each NoData pixel to the nearest pixel with a value
- can be seen as similar to vector buffers

Question 12

How does the straight line allocation function work?

Answer 12

assigns each cell the value of its nearest source
- helpful because identifying the closet proximity is often used as a simple method of filing data gaps
- objects need to be defined as integer values
- same as Thiessan polygons

Question 13

How does the straight line direction function work?

Answer 13

• computes the direction to the nearest source

Question 14

What is a kernel

Answer 14

A window of 3x3 pixels

Question 15

How do you move a kernel

Answer 15

A mathematical operator will move it over 1 cell at a time, this delivers a new value for each central cell under window, thus producing an entirely new grid
- each time the cell moves over it gets a new value, so by the end the whole thing is different

Question 16

Why is moving windows important?

Answer 16

• This process is the basis for spatial filtering
• you can highlight or suppress features in a layer based on spatial frequency (which is related to the texture, tone, or content of a grid)
• make something smoother or rougher

Question 17

What is filtering?

Answer 17

The use of neighbourhood functions on a grid to achieve a certain modification on the output grid

Question 18

What is the goal of low pass filtering

Answer 18

To let low frequency information pass through the filter, while high frequency information is subdued or removed
- abrupt changes are smoothed, homogenous areas remain as they are
- designed to emphasize larger, homogeneous areas
- sometimes used to get rid of speckle
-typical kernel choices: average, median, mode, majority

Question 19

What is the goal of high pass filtering?

Answer 19

Let high frequency information pass through the filter, while low frequency information is amplified
- boundaries are sharpened
- outliers are emphasized
- surfaces become rougher
- typical kernel choices: min, max, minority, range