Latest Contributions by EricKrause

So you already have a polygon feature class with a field indicating the slope? If that's the case, then right-click the layer in ArcMap, and open properties.  Under the Symbolization tab, click "Quantities" on the left, then "Graduated colors."  For the Value field, give it the field containing slopes, then select a Color Ramp that you like.  Then click Classify.  Change Classes to 1 and Method to Manual.  On the right, click on the Break Value, and type 15.  Click Ok. This should symbolize all polygons below 15% slope as one color and all polygons above 15% as another color. Does that answer your question? ... View more

Good to hear you found the tool.  I highly recommend using it to aggregate predictions to polygons. When researchers talk about block kriging, they're usually talking about things that are a lot more complicated than just averaging to polygons.  They usually are talking about analyzing how the point-to-point semivariogram compares to the polygon-to-polygon semivariogram after doing areal averaging of the discretized surface.  But if you just want to aggregate kriging predictions to polygons, you don't really need to worry about all that. ... View more

Does your Geostatistical Analyst toolbox look like the picture I've attached? And yes, block kriging is just taking averages of predictions within the areal regions. ... View more

Thank you Eric for helping me understand the areal prediction details. To my knowledage, when interpolating a surface from say ordinary kriging, the default is filled contour display; but when further predicting to arbitrary areal unit, you mean the gridded cell values are averaged per area/block? So even when the surface looks continous, the underlying predicted values are still cell-discretized (for a cell size of my choice i understand)? The filled contour display is just for visual representation.  The surface actually is continuous, but in order to make areal predictions, the surface is discretized.  This is true for both block kriging and geostatistical simulations. And a separate question, when the areal units are variable in size, do larger areal units have higher prediction uncertainty (or higher estimated variance), or lower? Thanks again for your insight! I will have to make do with GA for now since i don't have a GGS license... GGS is a tool in the Geostatistical Analyst toolbox (in the Simulation toolset), so if you have a GA license, you have access to the tool.  The tool was added in ArcGIS 9.3. In general, larger areal units will have smaller standard errors from both block kriging and geostatistical simulations. ... View more

This is a bit outside my area of expertise, but I'll give you my thoughts (you might have better luck on the Spatial Analyst forum). You need to think about how you want to define slope for a polygon.  Do you just want to average the slopes within each polygon?  Or do you want to find the maximum slope within the polygon?  Or something else? Almost certainly, you're going to want to use the "Zonal Statistics as Table" tool in the Spatial Analyst toolbox, but you need to think about how you want to define the slope of an entire polygon.  Once you make the table using MEAN or MAX (or another criteria you decide), join the table to the tax parcel polygons.  You can then select all tax parcels with a slope above 15%. ... View more

Good to hear.  Without knowing the exact problem, I can't say for sure, but this has likely been fixed since 9.3. ... View more

Ok, we've talked it over, and we're going to change the graphic and some of the text from that topic.  The 10.0 web help will update, and it will be changed in a future service pack as well as in version 10.1. Thanks for bringing this to our attention. ... View more

GA Layer to Grid employs block kriging where the raster/grid cells are the "areal units."  We don't have block kriging to arbitrary areal units because GGS does the same job better.  If your goal is to predict to areal units, we highly recommend Geostatistical simulations over block kriging or zonal statistics. All GA Layer to Grid is doing is making predictions on a lattice within each raster cell, then taking the average of the predictions and assigning it to the raster cell.  By default, it only predicts a single point at the center of the raster cell, but you can specify the dimensions of the lattice (3 by 2, for example).  We recommend "Cressie, N (1993) Statistics for spatial data, Wiley, New York" for mathematical analysis of block kriging.  However, this book can be intimidating for people without a substantial background in statistics. For a more example-driven text that is tailored to Geostatistical Analyst and GIS users: http://esripress.esri.com/display/index.cfm?fuseaction=display&websiteID=194 Note: Neither GGS nor block kriging are "Bayesian" methods.  GGS can be called a Monte Carlo method (though that phrase is rarely used), and block kriging is simply areal averaging of the surface. ... View more

Good catch.  I think this may be a typo in our help.  I'll ask the author later today and get back to you. If nothing else, we shouldn't be calling them both kriging models because the model on the right is from Local Polynomial Interpolation, which isn't a kriging model. Thanks for the feedback. ... View more

Can you send your data to ekrause@esri.com?  I'll take a look and try to figure out what is causing the problem.  Thanks. ... View more

The best way to do this in Geostatistical Analyst is to use the Gaussian Geostatistical Simulations tool.  You first create a Simple kriging layer in the Geostatistical Wizard, then you use this layer as input to the GGS tool.  Make sure to condition on the features/field that you used to interpolate, then specify the statistical polygons where you would like to make areal predictions.  This process is conditionally simulating many point values in each of the polygons, then it's calculating statistics on these simulated points within each polygon. ... View more

You'll have to ask someone higher up the Esri chain than me.  I'm not supposed to talk about release dates.  Sorry. ... View more

Ok, I got the data, but I still can't trip the crash.  Were you using Windows 7? Maybe you need to reinstall Beta 1?  Or just wait for Beta 2 and see if it still crashes. ... View more

It doesn't look like the data got uploaded.  Can you try again or just send the zip to ekrause@esri.com? Thanks. ... View more

Daniel and I have talked over email, and to sum up the conversation, the problem is that he's fitting a linear trend, and he doesn't have very many data points. You can see in the two attached graphics that when the searching neighborhood moves away from the large value, the extrapolated predictions actually go up.  It's counter-intuitive that removing a large value causes predictions to increase, but you can get artifacts like this when you don't have many points. ... View more