PrintInterpolation is one of the most important methods of spatial analysis. Many methods of spatial interpolation exist, all of them based to some extent on the principle that phenomena vary smoothly over the Earth’s surface and Tobler’s First Law of Geography. Essentially, interpolation methods are useful for estimating values from a limited number of sample points for locations where no samples have been taken. In this lesson, we will examine several interpolation methods.
Learning Outcomes
By the end of this lesson, you should be able to
- explain the concept of a spatial average and describe different ways of deciding on inclusion in a spatial average;
- describe how spatial averages are refined by inverse distance weighting methods;
- explain why the above interpolation methods are somewhat arbitrary and must be treated with caution;
- show how regression can be developed on spatial coordinates to produce the geographical technique known as trend surface analysis;
- explain how a variogram cloud plot is constructed and informally show how it sheds light on spatial dependence in a dataset;
- outline how a model for the semi-variogram is used in kriging and list variations on the approach;
- make a rational choice when interpolating field data between inverse distance weighting, trend surface analysis, and geostatistical interpolation by kriging;
- explain the conceptual difference between interpolation and density estimation.
Checklist
Lesson 6 is one week in length. (See the Calendar in Canvas for specific due dates.) The following items must be completed by the end of the week. You may find it useful to print this page out first so that you can follow along with the directions.
| Step | Activity | Access/Directions |
|---|---|---|
| 1 | Work through Lesson 6 | You are in the Lesson 6 online content now and are on the overview page. |
| 2 | Reading Assignment | The reading this week is again quite detailed and demanding and, again, I would recommend starting early. You need to read the following sections in Chapters 6 and 7 in the course text:
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| 3 | Weekly Assignment | Exploring different interpolation methods in ArcGIS using the Geostatistical Wizard |
| 4 | Term Project | A revised (final) project proposal is due this week. This will commit you to some targets in your project and will be used as a basis for assessment of how well you have done. |
| 5 | Lesson 6 Deliverables |
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Questions?
Please use the 'Week 6 lesson and project discussion' to ask for clarification on any of these concepts and ideas. Hopefully, some of your classmates will be able to help with answering your questions, and I will also provide further commentary where appropriate.