Contouring data - Exercise 5.

A variety of software packages will plot, contour, visualize and analyze x,y,z data. We have used Surface 3 in the past, a Mac based, freeware program from the Kansas Geological Survey (which unfortunately has not been kept up to date). Enough advantages have accumulated that now we use Surfer, a PC commercial product, which is available in the DSC computer lab. The similarities between the two are significant, but Surfer has more options. In both cases you can learn enough in an hour or two to produce usable products, which is the purpose of this lab.

Once you have the data you can think of the process of producing a contour map with the computer as 5 fold:

a) getting the data into the right form (format is important).
b) gridding the data.
c) plotting/contouring the data.
d) making the product 'pretty' (i.e. read user friendly and informative).
e) getting the product in the right format.

Remember the help option ­ the documentation is decent for this program.

If you are having trouble finding appropriate data to plot, links to one data set are provided below, and other links are on the main page for this week's material . As incentive for finding your own data (which can take substantial effort) there is a 1 point bonus for doing so, and if it is a particularly good data set that can be added to the options for future students there are 2 bonus points that will be rewarded.

Getting the data in:
There a several ways to do this, and we will explore 2. The easiest is to have your data in an Excel spreadsheet as three columns of x, y and z data. The first row can be data labels (e.g. easting, northing and elevation). You can open this directly from the gridding option (see below). Keep it simple to start with, and only have your data on the sheet. If your data is originally in latitude and longitude you need to convert it to UTM in order to have a map without significant distortion. You can use this UTM-lat.long Excel sheet for the U.S. (no promises it works, and it takes some time to learn how to use it). Use NAD 83 for you geodetic datum when you make the conversions. For the many parts of the world you can download Excel calculators that will do the transformation for that particular part of the world.
The second option to enter your data is to open a tabular data sheet within Surfer. To do this Select File/New. Choose the worksheet option.You can copy and paste from Excel. Enter your data. You will need to save it as a file before you can access it from the Grid option. As you will see for one project Surfer can generate quite a few different types of files, and so file management is important. Making a folder for each map project is a good idea. Once you've entered and saved your data then you can close this window to get to the plotting window.

Gridding the data:
Select the Grid/Data option. Find the file you want to grid, and select it. You should be able to grid directly from your Excel file, although you will have to tell Surfer what sheet in the file the data is in. Note that you must save the data as a grid file that you will access from the Map option. When working on one project you will likely have a minimum of 3 files: a data file, a grid file, and a plot file. Get used to it. ArcGIS, a software package we will explore later, produces a plethora of files, and to reiterate, for large projects file management is an important issue. Note that in the window in Surfer that opens you have a variety of gridding options. The kriging option is the default one, although in this exercise you will look at some of the others. As you explore the different gridding options you will see that the gridding option you use is important. Your reading, and lecture notes should give more insight into the different gridding options. Note that a report is produced when you grid the data. Familiarize yourself with the information provided in the report (yet another file you can save).

Contouring the data:
Once you have a grid file you can contour it, or create wire-frame models, or a variety of other outputs. For this exercise you should try all except the base map option and the vector option. Note the Map/3Dview option. Once you have created a map and selected (click on it so the 'handles' are evident), one can then change the perspective with this option. There are a variety of plotting options. Note that this works on other 'maps' than the wire frame. You can also produce a posting map, which shows the location of the data points, so that the viewer can see what the spatial distribution of the data that underlying the contouring results is. This is very useful and almost routine.

Making the product 'appealing':
In the interest of time we will not focus on this aspect in this lab. Nonetheless, it is important to make your products user friendly and informative (appealing in this case does not mean gaudy colors). Obviously, the map should be well labeled so that the reader knows what they are looking at. In addition, Surfer allows you to color and customize your maps in a great variety of ways. If you have the time and interest you can explore some of these options.
One other cautionary note. With such high powered software one can make the map look better than it should, perhaps giving the impression of false precision and/or accuracy. You should take pains to let the reader know what data the modeled surface is based on, and how that data has been processed. This is where the Post map option is important.

Getting the product in the right format:
If you want to include the map or plot in a word, document, or web site, or in some other software environment you may need to export the results as a file. Surfer will export images as AutocadDXF files, bitmaps, tiffs, jpegs and ESRI shape files. The Export option is under the file menu.

Your assignment this week is to find some x,y,z data of geologic significance and plot it. Many other possibilities exist. Remember that you are modeling some sort of presumed spatially continuous distribution of data and point phenomena such as earthquake will not work. Note that if your data comes with latitude, longitude position and you plot it as such, there will be significant distortion. Your best bet is to transform it into UTM coordinates of easting and northing. There is also a UTM calculator on the web that can do the transformation nicely, but the problem is you have to enter each data point one by one. There are different UTM zones, defined by different starting points, and you need to make sure all your data falls in the same UTM zone. Remember that a degree latitude is more constant in length, but lengths across longitude vary extremely as a function of latitude position and this distortion is especially pronounced in polar regions. Best to transform to UTM, or obtain the position data as UTM in the first place. Some databases will allow you to choose the type of location output. Try to get at least 40-50 points to plot.

Your final project should consist of:
a) a copy of at least part of your data, along with a description of the data and the data source.
b) a Post map showing the labeled data points.
c) a contour map where the kriging option was used (labeled as such).
d) 2 contour maps where another gridding option was used. You will need to save yet other grid files.
e) a paragraph describing how the resulting contour maps differ and why. Indicate which gridding routine you think produces the best results.
f) a wire frame diagram of the contour map you think most representative.
g) a shaded relief map of the same contour map.
h) a discussion of the scientific significance of your map.

If you are having trouble finding data the following is from a detailed gravity survey of a valley in Idaho:

Other data sets to use or play with:

Don't hesitate if you have any questions. Cheers!