geostatistical-analyst-tutorial.pdf

Geostatistical Analyst Tutorial

Geostatistical Analyst Tutorial

Table of Contents

Introduction to the ArcGIS Geostatistical Analyst Tutorial . . . . . . . . . . . . . . . . . . . 3

Exercise 1: Creating a surface using default parameters . . . . . . . . . . . . . . . . . . . 6

Exercise 2: Exploring your data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Exercise 3: Mapping ozone concentration . . . . . . . . . . . . . . . . . . . . . . . . . 32

Exercise 4: Comparing models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Exercise 5: Mapping the probability of ozone exceeding a critical threshold . . . . . . . . . . . . 51

Geostatistical Analyst Tutorial

Introduction to the ArcGIS Geostatistical Analyst

Tutorial

With ArcGIS Geostatistical Analyst, you can easily create a continuous surface, or map, from measured

sample points stored in a point feature layer or raster layer or by using polygon centroids. The sample points

can be measurements such as elevation; depth to the water table; or levels of pollution, as is the case in this

tutorial. When used in conjunction with ArcMap, Geostatistical Analyst provides a comprehensive set of tools

for creating surfaces that can be used to visualize, analyze, and understand spatial phenomena.

Tutorial scenario

The U.S. Environmental Protection Agency is responsible for monitoring atmospheric ozone concentration in

California. Ozone concentration is measured at monitoring stations throughout the state. The locations of

the stations are shown here. The concentration levels of ozone are known for all the stations, but the ozone

values for other (unmonitored) locations in California are also of interest. However, due to cost and

practicality, monitoring stations cannot be placed everywhere. Geostatistical Analyst provides tools that

make optimal predictions possible by examining the relationships between all the sample points and

producing a continuous surface of ozone concentration, standard errors (uncertainty) of predictions, and

probabilities that critical values are exceeded.

Geostatistical Analyst Tutorial

The data required to complete the exercises is included on the tutorial data DVD. When you run the wizard

to install this data, check to install the Geostatistical Analyst data (the default installation path is

C:\ArcGIS\ArcTutor\Geostatistical Analyst). The following datasets (which are contained in a geodatabase

called ca_ozone.gdb) will be used in the tutorial:

Dataset

Description

ca_outline

Outline of California

O3_Sep06_3pm

Ozone point sample values (ppm)

ca_cities

Major California cities

ca_hillshade

A hillshade map of California

The ozone dataset (O3_Sep06_3pm) was provided courtesy of the California Air Resources Board and

represents the concentration of ozone measured on September 6, 2007 between 3:00 and 4:00 p.m. in parts

per million (ppm). The original data has been modified for the purpose of the tutorial and should not be

considered accurate data.

From the ozone point samples (measurements), you will produce two continuous surfaces (maps) predicting

the values of ozone concentration for every location in the state of California. The first map that you create

will simply use all the default options to introduce you to the process of creating a surface from your sample

points. The second map that you produce will allow you to incorporate more of the spatial relationships that

are discovered among the points. When creating this second map, you will use the exploratory spatial data

Geostatistical Analyst Tutorial

analysis (ESDA) tools to examine your data. You will also be introduced to some of the geostatistical options

that you can use to create a surface, such as removing trends and modeling spatial autocorrelation. By

using the ESDA tools and working with the geostatistical parameters, you will be able to create a more

accurate surface. Many times, it is not the actual values of some critical health risk that are of concern but

rather whether the values are above some toxic level. If this is the case, immediate action must be taken.

The third surface you create will assess the probability that a critical ozone threshold value has been

exceeded. For this tutorial, the critical threshold will be if the value of ozone goes above 0.09 ppm

(California State's ambient air quality standard for hourly measurements); then the location should be closely

monitored. You will use Geostatistical Analyst to predict the probability that ozone values across California

complied with this standard on September 6, 2007 between 3:00 and 4:00 p.m.

This tutorial is divided into individual tasks that are designed to let you explore the capabilities of

Geostatistical Analyst at your own pace.

• Exercise 1 takes you through accessing Geostatistical Analyst and the process of creating a surface

of ozone concentration using default parameter values to introduce you to the steps involved in

creating an interpolation model.

• Exercise 2 guides you through the process of exploring your data before you create the surface to

spot outliers and recognize trends.

• Exercise 3 creates a second surface that incorporates more of the spatial relationships discovered in

exercise 2 and improves on the surface you created in exercise 1. This exercise also introduces you

to some of the basic concepts of geostatistics.

• Exercise 4 shows you how to compare the results of the two surfaces that you created in exercises

1 and 3 and how to decide which surface provides the better predictions of the unknown values.

• Exercise 5 takes you through the process of mapping the probability that ozone exceeded a critical

threshold, creating a third surface.

You will need a few hours of focused time to complete the tutorial. However, you can also perform the

exercises one at a time if you want. It is recommended that you save your results after each exercise.

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