Assignment 8: Surface Interpolation and Analysis
Due March 16, 2012
Introduction
Researchers in many natural and social sciences are faced with the task of examining the spatial
distribution of some phenomenon or feature. It is usually impossible to measure those phenomena or
features everywhere. This is especially true for continuous phenomena such as temperature, soil
moisture or even levels of crime in an urban area. This issue is resolved by designing a sampling
approach that would allow the researcher to capture as much of the variation in the feature or
phenomenon over the study area as possible. After the data is collected at the sampled locations, the
next step is to turn this discrete data into a continuous surface which would help to visualize and
understand the patterns of variation exiting in the feature or phenomenon of interest.
Surfaces describing variation of phenomena or features over a certain area are produced using
interpolation methods. In this assignment you will learn how to run interpolation procedures using
Spatial Analyst Extension of ArcGIS 10 and interpret their results. You will also perform several simple
analyses that are applied to mostly terrain surfaces. The practical part of the assignment consists of the
guided tutorial based on selected sections of the ESRI web course Learning ArcGIS Spatial Analyst
followed by an ‘on your own’ section.
Section 1: Theory
Textbook readings: Chapter 6
Answers to the questions below can be found in the textbook, ArcGIS Help files, the guided tutorial, or in
other sources online. After consulting the sources you find, please provide the answers in your own
words. If you use somebody else’s wording, please reference the source.
Each question is worth 5 marks
Note: The questions may be easier to answer after you have done the Guided Tutorial section.
1. Please describe how the hillshading technique works (Note: you do not need to provide specific
equations used to calculate the hillshading.)
2. In the table below, describe and compare the four surface interpolation methods you have
worked with in this assignment.
Interpolation
method
Short description of
the method
What could it be
used for?
Is it a local or a
global
interpolator?
Is it an exact or
approximate
method?
Is it a stochastic
or deterministic
method?
IDW
Spline
Natural Neighbours
Kriging
1|Page
Section 2: Guided Tutorial
In this section of the assignment you will continue working on the ESRI web course Learning ArcGIS
Spatial Analyst.
Instructions
1. Go to: http://training.esri.com and select My Training from the left-hand menu.
2. Select My Virtual Campus Courses and then log in using the username and password you created
when you worked on Assignment 1.
3. Under Courses in Progress heading, click on the title of Learning ArcGIS Spatial Analyst course to
get back to this course.
4. Make sure that the data you need to complete the exercises in this course is saved to your H:\ drive
or any other drive you have a permission to write to, so that when you create or modify the datasets
you would be able to save these changes.
5. In Module 2, complete the Calculate Hillshade exercise in the section Visualizing surface data and
all three exercises in the Deriving data from surfaces section.
6. In Module 4, complete the Introduction to interpolation section.
7. You do not need to submit results of your work for this section of the assignment. However, you
will rely on the skills you learned in this section to complete the ‘on your own section’ that follows.
Notes:

In Step 1 of all the exercises (titled Open the map document), check the environmental settings
to make sure they are set to the parameters specified in the text of the exercise.
All the settings mentioned in this step are represented by separate options in the Environment
Settings dialogue box:

Tutorial
ArcGIS 10
Current workspace
Workspace
Scratch workspace
Workspace
Extent
Processing Extent
Raster Analysis Settings
Raster Analysis
I would advise you to check out the theory sections in the Interpolation methods section of
Module 4. Information provided there may be useful for answering Question 2 in this
assignment.
2|Page
Section 2: On Your Own
In this part of the assignment you will try your hand at surface interpolation and analysis. Fist you will
analyze terrain in Greenwood County in southwestern Alberta. Then you will use surface interpolation
methods to analyze income distribution in the City of Regina. Datasets you will be working with are
located in T:\Class\Geography\geog303\Assignment 8 folder.
Terrain Analysis
1. If necessary, start ArcMap and add greenwood_dem raster dataset from the Assignment 8 folder to
the map document.
2. In the Layer Properties dialog box, change the symbology of the dataset from Stretched to
Classified. Set the Colour Ramp to Elevation #1. To make finding the colour ramp you need easier,
right-click on the current choice of the ramp and turn the Graphic View option off.
You may also need to change the label values for this layer to integers. This is done by clicking on
each label and typing in the desired text. Click OK to apply the formatting to the greenwood_dem
dataset and to close Layer Properties dialogue box.
3. Set the following environment settings:
Current workspace
Assignment 8 folder with the data for this assignment
Scratch workspace
Assignment 8 folder with the data for this assignment
Output coordinates
same as layer greenwood_dem
Processing extent
same as layer greenwood_dem
Cell size
same as layer greenwood_dem
4. If the Spatial Analyst extension has not been activated, to do so from the Customize menu choose
Extensions option. When the Extensions dialog box opens, check the Spatial Analyst check box and
click Close.
5. Calculate hillshading, slope and aspect for the greenwood_dem terrain surface
6. Using the results of your analyses, describe the elevation pattern in Greenwood County.
Note: aspect function allows you to see which way the slopes are facing, but does not at all reflects
the steepness of the slopes.
Question 3: Description of the elevation pattern in Greenwood County
3 marks
7. Using the technique you learned in the Calculate Hillshade exercise in the Guided Tutorial section,
create a shaded relief map of Greenwood County. Use LetterLandscape template making
adjustments to the size and appearance of the map elements as needed.
3|Page
Question 4: Submit a shaded relief map of Greenwood County
5 marks
Surface Interpolation
1. If necessary, start ArcMap and add the following datasets from the Assignment 8 folder to the map
document:
reg2006da_nonzero – a dataset containing points at which the income data was collected
across the city
ReginaCity2006NBH_UTM – a dataset containing Regina neighbourhood boundaries
To make the point dataset visible, in the Table of Contents move it above the neighbourhood
boundary dataset by clicking on it and dragging it to a desired position.
2. Open the attribute table of the reg2006da_nonzero dataset and examine its fields. The table
contains the following attributes:
Attribute
Description
DA
A unique identifier of a sampled area
Population
Below_LICO
Total population of a sampled area
Proportion of an area’s residents that
self-identify as Aboriginal
Proportion of an area’s residents
living below a low income cut-off
Median_inc
Median household income in an area
Average_in
Average household income in an area
Aboriginal
Close the attribute table.
3. Examine the distribution of points in the Map Window. It appears that some neighbourhoods were
sampled more than others. To get a complete picture of the income distribution in Regina you will
estimate the income values at unsampled locations using two surface interpolation methods,
Inverse Distance Weighted and Kriging.
4. Before you begin the analysis, set the following environment settings:
Current workspace
Assignment 8 folder with the data for this assignment
Scratch workspace
Assignment 8 folder with the data for this assignment
Output coordinates
same as layer ReginaCity2006NBH_UTM
Processing extent
same as layer ReginaCity2006NBH_UTM
4|Page
Cell size
Maximum of inputs
5. Run the IDW Tool using the reg2006da_nonzero dataset as the input and Median_inc as the z-value
field. Change the default setting for Power to 3 and for Number of points to 6. How does this affect
the IDW procedure? Why in this case would we want to have these parameters set more
conservatively?
Question 5: 2 marks
6. Next run the Kriging Tool using the reg2006da_nonzero as input and Median_inc as the z-value
field. Change the default setting for Number of points to 6.
7. Examine the resulting surfaces. To make the examination easier, in the Table of Contents move the
neighbourhood boundary dataset to a position below the reg2006da_nonzero layer.
Open the Properties dialog box for this layer. In the Symbology tab, click on the Symbol Selector (a
big button coloured the same colour as the polygons in this layer); in the window that opens, click
on the Fill Colour button and set the layer fill to No fill. Click OK and OK to apply the change and
close the dialogue box.
Position the surfaces under the neighbourhood boundaries layer. You can examine and compare
the patterns present in the surfaces by:



Turning them on and off to visually compare the pattern
Using the Identify Tool to find out names of the neighbourhoods; this will help you to tie the
surface patterns to the real world
Using the Identify Tool to find out the values at the sampled areas to see how closely they
correspond to the interpolated values in the surfaces.
8. Based on what you see, describe the general pattern of distribution of the median household
income across Regina neighbourhoods. In which neighbourhoods the median household income
tends to be the highest? In which the lowest? Where are these neighbourhoods located in relation
to the centre of the city?
Question 6: Description of the pattern of the median household income distribution in Regina
3 marks
Question 7: Which of the two interpolation methods provides more realistic results?
1 mark
9. Create a map showing results of surface interpolation using the two methods. For this you will use
the TwoDataFrames template you worked with in one of the first assignments.
Open the empty TwoDataFrames map document located in the Assignment 8 folder. To populate
this document and create a map showing results of both the IDW and Kriging interpolation, copy
layers in your working map document and paste them in each of the two empty data frames in the
TwoDataFrames document.
To do that:
5|Page




In the Table of Contents of your working map document, hold the Control key down and
click on the reg2006da_nonzero, ReginaCity2006NBH_UTM layers and the layer containing
the results of IDW interpolation.
Release the Control key, then right-click on the selected layers and choose Copy.
Switch to the TwoDataFrames map document. Right-click on the top empty data frame and
choose Paste Layers. The selected layers get transferred to the TwoDataFrames map
document.
Repeat the same steps for the reg2006da_nonzero, ReginaCity2006NBH_UTM layers and
the layer containing the results of Kriging.
Adjust the size and position of the map elements as needed and export your map into .jpg format.
Submit a map showing results of your interpolation analysis
10 marks
6|Page