Geostatistical analyst layer

[ErnestDunwoody]

can any one tell me how to create a geostatistical analyst layer?

Sorry to have to ask such a dumb Q but ArcMAP help was helpless, yet again, on this topic.

Using the Create Geostatistical layer Toollbox requires a Geostatistical model source and an input layer.

What is this Model source? A misleading name for an ordinary layer or is it something else? Where do you get or create it?

The next box wants an Input dataset but I can't get anything to go in there, probably because the Layer I put in the first box doesn't have what it is needed. 

Sure would be helpful if the Arc Map tool help files contained helpful information.

Sincerely,
edi151

[XIANWANG]

Hi, Erik

I have another question for Kringing Geostatistical Wizard. Can I set the lower and upper values for the results of Kriging interpolation? Thanks!

[EricKrause]

No, you cannot control the maximum (or minimum) value of the interpolation.  Whatever the maximum is (if there even is a maximum) will come from the kriging equations.  These equations are constructed based on all the provided parameters, and the maximum/minimum will be whatever the equations say they are.

In fact, if we could detect the maximum and minimum, my life would be a lot easier.  Currently, we symbolize geostatistical layers based on the min/max of the input data, not the actual interpolation.  If we knew the min/max of the interpolation, we could symbolize the geostatistical layer based on these values.  If you have ever noticed that geostatistical layers often look very different after being exported to raster, it is because of this issue.  If we could detect the min/max of the geostatistical layer, we could make the symbology closely match the raster.

[XIANWANG]

Thanks a lot. Yes, I find the the range of geostatistical layer is different from the raster one. So now I am thinking if I can set the range of geostatistiacal layer. What I mean is that I got the geostatistiacal layers, and I will set the range of these geostatistiacal layers, for example the minimum is 0, then I can use GA Layer To Points tool to get the values  of the points, which supposed to be larger than 0.

[EricKrause]

After reading your post again, it sounds like you are trying to convert a layer into a geostatistical layer.  That can't be done.  A geostatistical layer can be exported to a raster but not the other way around.

[ErnestDunwoody]

Thank you very much for offering to help. I've read the Help files extensively but am having trouble getting started. I have a modest classical statistical background.

What I seem to have stumbled across so far is that you can use Geostatistical Analyst/Explore Data to get an insight into the spatial distribution of point vector data and you can convert raster layers into geostatistical layers using the Geostatistical Wizard in Geostatistical Analyst. Then you can use these Geostatistical Layers as input to the Geostatistical Tools in Arc ToolBox. Am I right so far?

I have two tasks.

1. I need to find the strength of association between my species distribution data (Greater Bilby distribution features such as burrows, feeding sites, fecal pellets etc) and a number of features in the landscape that I have analysed such as landcover class, elevation, aspect, soil type, soil density, soil texture and pH. I can do these by a series of spatial joins on pairs of data and extract the positive joins and count them and build up a table of frequencies this way. Long and tedious. No measure of the covariance. Was wondering if I could analyse the strength of association between each species feature and the landscape features using Geostatistical Analyst somehow?

2. In another project I have to develop measures of the directional variance of specific landscape features (e.g. clumps of trees, clumps of shrubs etc) for different landscape types. Basically I want to know the minimum transect length I have to use in each cardinal direction in each landscape type to capture 95% of the variance in the landscape. What I was hoping to do was to analyse the images into indices, e.g. NDVI as a simple example, and then measure the frequency of different sized NDVI clusters in each direction using semivariograms. How would I do this? Do I have to classify the NDVI pixel values into objects, create polygons out of each type and size class and then anayse the ditribution of polygon centroids? I was hoping I could do it by analysing the distribution of the raster of Indice values.

Thank you for your interest in my request. I will very much appreciate your advice.
Sincerely,
edi151



What I would now like to do is to get a measure of the directional variance of the landscape cover data.

[EricKrause]

Sorry for the delay in response.  You caught us on a particularly busy week.

I think you may have a few misconceptions about what Geostatistical Analyst is and what it can do.  I'll do my best to clear up any confusions.

What I seem to have stumbled across so far is that you can use Geostatistical Analyst/Explore Data to get an insight into the spatial distribution of point vector data and you can convert raster layers into geostatistical layers using the Geostatistical Wizard in Geostatistical Analyst. Then you can use these Geostatistical Layers as input to the Geostatistical Tools in Arc ToolBox. Am I right so far?

Geostatistical Analyst deals almost exclusively with interpolation methods, with special emphasis given to kriging.  Many variables change continuously across space (like temperature and elevation).  The goal of interpolation is to predict the value of the variable at any location based on measurements taken at particular locations. 

The general workflow is to start with point vector data, where each point contains a measurement of the variable at that location.  Before proceeding with interpolation, the Exploratory Spatial Data Analysis (ESDA) tools allow you to explore the structure of your data.  You can see histograms, apply transformation, explore trends, etc.  Note that these "tools" are not geoprocessing tools (they are not in ArcToolbox); they are GUI-based and interactive, and they're found in the Geostatistical Analyst toolbar. 

Once you are satisfied that your data is appropriate for interpolation, the points are used as input for the Geostatistical Wizard.  Inside the Wizard, the GUI environment allows you to visually fit an interpolation model (interpolation methods like kriging have many parameters, and the quality of your predictions depends on the quality of your model).  The Wizard provides many interactive diagnostics for fitting an appropriate model. 

When you are satisfied with the model, the output of the Wizard is a geostatistical layer.  This layer is a smooth surface of predictions for the variable.  It is visualized as a contour map, but the predicted value of the variable can be calculated at any point on the surface.

Geostatistical layers are different than raster layers in that they are dynamic.  A geostatistical layer contains all the information it needs to make predictions at any specified location, but it doesn't actually store the predictions themselves.  Instead, it stores the mathematical model needed to make the predictions, and then it calculates them when you ask it to. 

Geostatistical layers can be converted to raster, and this is done by simply applying the mathematical model to the center of each cell in the raster.  Ignoring memory and time constraints, you can make the cell size of the raster as small as you want.

You cannot convert a raster layer into a geostatistical analyst layer because the resolution of the raster is limited by the cell size, whereas geostatistical layers have infinite resolution (limited only by the precision of the computer).  You could, however, convert the raster to points, then use these points to build an interpolation model in the Wizard.  The Wizard would then create a geostatistical layer from the model (though I would be very cautious before doing this). 

The tools in the Geostatistical Analyst toolbox are generally used for post-processing after a geostatistical layer is created in the Wizard (such as converting a geostatistical layer to a raster or getting predictions for a set of points).  In addition, the interpolation methods that do not require a high level of interactive model fitting are offered as tools.  Like the Wizard, they take point vector data as input and produce geostatistical layers of predictions.

All that being said, it doesn't sound like interpolation is what you need.  I wish I could be more help, but my specialty is interpolation, and I'm just not sure how to go about solving your particular tasks.  You may want to look into Geographically Weighted Regression, which is available in the Spatial Statistics toolbox.

Let me know if you have any other questions, and I'll do my best to help.