More Geoprocessing & Modelbuilder

Question 1

What is a key component of any analysis, especially suitability?

Answer 1

The ability to transform data to fit the factors
- Vector to raster
- Weighted overlays
- Reclassification
- Interpolation, polygons, IDW
etc.

Question 2

Why is it valuable to be able to store frequently used tools and models in a geodatabase?

Answer 2

• Easy sharing with other users

- Efficiently access frequently used tools w/o having to search for them each use

Question 3

Why isn’t raster calculator used for weighted overlay (even though it can do the job)? What can be used instead?

Answer 3

• Raster calculator doesn’t work in a model environment

- Use weighted overlay tool instead

Question 4

What do Thiessen Polygons do? Abrupt or Gradual?
Exact or Approximate?
Global or Local?

Answer 4

• Converts Points to polygons
• One polygon per point
• Every spot in the polygon is closer to that point than any other
• Abrupt, no gradient
• Exact, honours original data, #’s don’t change
• Local, no influence from points further away than neighbours

Question 5

How do Thiessen Polygons work?

Answer 5

• Connect each point to its nearest neighbours
• Draw perpendicular bisector of these connecting lines
• Connect all bisectors and remove the lines connected the nearest neighbours

Question 6

Inverse Distance Weighting (IDW)

Answer 6

• unknown value of a field at a point is estimated by taking an average over proximal known values
• Over-used and ill-used

Question 7

How are proximal values to evaluate determined by for IDW?

Answer 7

• determined by specified distance (radius, number of cells)

- Sectors

Question 8

What are some of the 1st steps to a suitability analysis?

Answer 8

• Carefully examine study parameters
• -Extent, Constraints
• Edit supplied data
• -Deleting, Buffering, Clipping

Question 9

How does the Vector to Raster Tool and Cell Assignment Type relate to uncertainty?

Answer 9

• Check ArcHelp…

- Cell Centre makes sure majority of vector is in the cell

Question 10

What part of the toolbox does the Weighted Overlay tool reside?

Answer 10

• Spatial Analyst Tools

Question 11

Why should data be reclassified to the same relative scale?

Answer 11

• To aggregate the data

- Don’t want to be comparing apples to oranges so to speak (13m to 27m for example)

Question 12

How does the model show that a tool/process has been run?

Answer 12

• Tools and outputs have a dropped shadow underneath

Question 13

What are Eigen Vectors in AHP?

Answer 13

• Calculate weights statistically and scientifically based on matrix of importance

Question 14

What has happened when something in the model has gone red? How is this useful?

Answer 14

• Something has gone wrong

- Makes it easy to find errors

Question 15

What can be done to fix an output if an interpolation has extended too far?

Answer 15

• Clip it to study area extent

Question 16

How are proximal values determined by in IDW?

Answer 16

• Specified distance of radius or number of cells

- Sectors

Question 17

What happens with the weights of points when using Inverse Distance?

Answer 17

• Weights decrease with distance

Question 18

Tobler

Answer 18

• Things that are close together are likely to be similar

Question 19

What is the weighting function for IDW? What is the smoothing aspect of the function?

Answer 19

Weight (d) = 1/d^x

Smoothing function is x

Question 20

What is the default of x in the weighting function of IDW? What happens when the number is increased?

Answer 20

2 is default

• When x is increased, the more influence the closer values have
• Higher the x, the less smooth the surface is

Question 21

What is the size of the neighbourhood for IDW?

Answer 21

Points or actual radius

Question 22

What is the result of an IDW?

Answer 22

• A continuous raster surface

Question 23

What are the important fields in an IDW tool?

Answer 23

• Input points
• Z Field
• Search Radius
• Polylines
• Output cell size

Question 24

Deterministic

Answer 24

• Uses data range of input points for interpolation range (employs only ‘your’ data)
• No interpolation will go below lowest, or above highest
• IDW uses this

Question 25

Is IDW abrupt or gradual?
Exact or approximate?
Global or local?

Answer 25

• Gradual, continuous surface of values
• Exact, because it is deterministic and honours inputs buy not going outside of input range
• Local, uses proximal values

Question 26

IDW edge effects? Issues with IDW?

Answer 26

• No value can be calculated outside of the range of input values
• May not reach full study extents
• Need points outside of study area in order to increase extents and fill area

Question 27

How can IDW edge effects be fixed?

Answer 27

• Needs representative number of input points

- May need outside of study area so surface extent covers entire study area

Question 28

What kind of data can have spatial interpolation? Which can have only density? Why?

Answer 28

• Interpolation can be used on data that is not discrete, but is gradual or spreading (pollutants)
• Density is used on discrete values (building heights) because it would not have a range of values between points