Objective: The objective of this lab is to expose you to some of ArcMap's interpolation capabilities, i.e., to experiment with interpolating a raster surface from a set of measured points. Several ways to do this (IDW, Spline, and Kriging) are provided via the spatial analyst toolset and a TIN-based approach is available through 3D Analyst. In this lab you will:
Use any of the datasets below. The data are in the usual place, now on Laulima.
ArcMap has several Spatial Analyst Tools to make raster data. This time, use Spatial Analyst Tools -> Interpolate to Raster-> (and choices of IDW, spline, and kriging) to interpolate raster maps from the sample data. Try all three methods and experiment with the interpolation parameter settings. Be sure to interpolate using the 'z' field, not the 'x' or the 'y' fields. (Why can't it figure that out?)
Visually and mathematically (via the raster calculator)
compare three surfaces (from those you created).
Use Spatial Analyst -> Raster Calculator to compute
[surface1] - [surface2]
i.e., a difference surface, in which to see where, and by how much, the interpolation results differ. (Does changing the exponent or the search radius in IDW interpolation have the effects that you expect from the text and lectures?)
For fullness, also generate a TIN from these data. From the 3D Analyst tool, use Features to TIN to generate the TIN, then the TIN to raster will give you a surface linearly interpolated on each triangular facet. (Does this produce the same surface you would get with IDW by setting the exponent to "1" and the neighbors to "3"?)
I haven't stressed cartographic presentation in this course, but we need to at least touch on Arc's "layout view". The basic idea in the current version of Arc is to have a "Layout View" into which are inserted objects that might be titles, map frames, tables, text blocks, scales, north arrows, and other elements that can be dragged around and modified.
It's all very click-n-drag-n-drop and probably faster to learn through experimentation and the help functions than through a slap-dash step by step handout. Try View -> Layout and then "insert" and position a few elements. (Like a title, some map frames, a text block, etc.) Note that you may need to drag things in the table of contents to newly created 'frames' for them to show-up.
Help - is on the main menu, and by now you should be getting comfortable using it.
Read ESRI's descriptions of these interpolation schemes.