Lesson: Creating a Geologic Map in ArcView

About the lesson:

In the previous lesson you learned to make a simple map by digitizing shapefiles over a GeoTiff Image. In this lesson, you will focus more on map presentation. Maps are one of the primary ways in which geologic information is communicated, and proper formating ensures that errors in communication are reduced. Besides, a well drawn map is very pretty.

Your task will be to create a map based upon a bedrock geology map published by the USGS. Such a task might occur in your research or work when you are interested in only a portion of the information already present in a GIS database. Although the amount of information in the new map will be reduced, you will create a map which clearly and completely presented.

About the Example Site:

This lesson concerns bedrock within the Mirror Lake Watershed, located within the Hubbard Brook Experimental Forest (HBEF), in the White Mountain National Forest, near North Woodstock, Grafton County, New Hampshire. The shape files you will be working with are taken from the bedrock map documented in the U.S. Geological Survey Open-File Report 00-045, Version 1.1, By William C. Burton, Gregory J. Walsh, and Thomas R. Armstrong. The bedrock in the Mirror Lake area is a Silurian sillimanite-grade schist that has been extensively intruded by late Devonian granite. The schist and granite are cut by dikes of pegmatite of unknown age, possibly a residual differentiate of the granitic intrusions. All three rocks are cut by lamprophyre dikes of middle Jurassic and early Cretaceous age. At a road cut along Interstate Highway 93, directly east of Mirror Lake, the exposed bedrock consists of a complex suite of rock types. The granitic intrusions are present as dikes, irregular pods, and anastomosing fingers that range in width from centimeters to tens of meters. Pegmatite typically is in the form of dikes, centimeters to meters wide, that cross-cut both the schist and the granite. The lamprophyre dikes, having widths of centimeters to meters, are less common than the other three rock types in the Mirror Lake area.

Get the Sample Data:

Create a directory in your class work space (i.e./nsm/class/gly560/username) called geolmap. Create a directory in geolmap called "shapefiles". Copy all the shape files from the following directory into that Shapefiles directory:

/nsm/class/gly560/class/geolmap

Lesson:

Creating the Project

  1. Open ArcView with a new project. Save the project in the working directory as geolmap.apr .

  2. Under the Project menu, open the Properties dialog. Specify the working directory you will be using for this project as the "shapefiles" folder that you created. Most data you will produce will be shape files, so this will be the most convenient setting for this project.

  3. Create a new view, and name it Bedrock Map. Add all of the shapefiles to the view by clicking the button and then shift+selecting all of the shapefiles. Activate all of the themes and arrange them such that the point themes overlay the line themes, and the line themes overlay the polygon themes. You can move the themes around by clicking and dragging them.

  4. Gliding the cursor over the image, you will notice that in the upper right hand corner of the window the location coordinates are that of latitude and longitude. This is because these shapefiles are as yet unprojected, meaning they are still in geographic coordinates. You will learn about map projections in a later lesson.

  5. You will need to work with the legends to get a resonable display of the themes. Start with the contx.shp theme, which represents all of the bedrock geologic contacts. Activate the theme and use the Properties dialog to change the name of the theme to Bedrock Geology.

  6. We want to create a color scheme for all of the unique bedrock unit identified in the map. Note that the traditional colors used on geologic maps are are actually set by agreement among the world's geoscientists. In the United States, the U.S. Geological Survey set a color standard for its first national geologic map in 1881. In general, these colors apply only to sedimentary rocks, and plain colors apply only to marine rocks. Sedimentary rocks that form on land are depicted with these colors plus patterns, such as dots or stripes. The other major rock classes—igneous and metamorphic—have their own color traditions. Reds and oranges are reserved for the igneous rocks: volcanics take orange while plutonics take red, and in both of these older rocks are shown with darker colors. Metamorphic rocks tend toward browns, olives, and other "complex" colors. All of them use patterns freely as well. As we are interested in metamorphic rocks here, we will use an olive to brown color scale. Double click on the Bedrock Geology them to open up the legend dialog box. Under Legend Type choose Unique Value and under values field choose Code. The legend should be populated by olives reds and browns corresponding to the various rock units.

  7. In keeping with the traditional color schemes, we want to change the legend to give plutonic rocks red colors, and make the younger metasediments lighter than the older metasediments. The codes listed in the legend, correspond to those used for the HBEF bedrock map. A close view of the legend from there map provides a description of all of these codes, and the corresponding color schemes. Notice that the devonian intrusive plutonic rocks Dg, Dp, are designated in bright red.

  8. Double click on the theme to open the Legend dialog box, and then double click on the symbol to open the Marker Palette. Click on the button and change the colors for Dg and Dp to strong red colors, making the older rock slightly darker. Repeat this process to make sure that the younger Silurian rocks are slightly lighter than the older Silurian rocks. Apply the changes and close the legend dialog box. Save the project.

  9. Give brief descriptions of all the bedrock units by typing text in the Label column. As the color codes themselves are cannot be labeled, label as Abbreviation: Description. Use the descriptions given in the HBEF map. Apply the changes and close the legend dialog box. Save the project.

  10. Give the other themes the names Hydrography, Faults, Roads, and Structure. Make the Hydrography cyan. Use the pen palette to the appropriate double-line symbol for roads with a line thickness of 1, and use the pen palette again to designate Faults as a solid black line with thickness 2.

  11. Geologic maps typically have may symbols that represent structural, mineral, hydrologic, topographic, and other features. These symbols are being standardized in digital form by the federal government. On the HBEF Bedrock Map there are many symbols for various types of structural features. For our map, we are interested only in differentiating between planar features which are described by strike and dip, and linear features which are described only by their trend. We will need to use special legend symbols to represent these geologic map features. Double click on Structure to open the legend dialog, and then double click on the symbol to open the Marker Palette. Click on the fonts button. Scroll down until you find the ESRI Geology font, select it, change the font size to 24, and then click on the Create Markers. Now click on the Markers button and scroll down until you see the geologic symbols you just added to the marker list. Now close the Marker Palette.

  12. From the Legend dialog box, choose a Legend Type of Unique Value, and from the Values Field chose Type. Different symbols will be assigned to linear and planar features. Change the label of the symbols to Linear Feature, and Planar Feature, respectively.

  13. Double click on the Linear Feature, click on the Markers button, and scroll down to choose the symbol. Change change the font size to 16, the color of the symbol to black. Click apply and then double click on the symbol for the Planar Feature. Choose the symbol for the Planar Feature, change the font size to 16 and change the color to black. Click Apply and close the Legend dialog.

  14. Note that the Structure features do not look right, because all of the symbols are oriented the same way. We can vary the orientation of these symbols if we wish. Open the legend dialog for the Structure theme. Highlight the symbol for Linear Feature and click the Advanced button at the bottom. In the dialog that opens, choose Symbol_Ang for the rotation field. Click OK to return to the legend dialog. Repeat the process for the Planar Feature. Click Apply and close the legend dialog box. The symbols should now be oriented according to their strike. Save the project.

  15. The ArcView project is now finished. What remains is to format the geologic map. Geologic maps vary in their content, layout, size, and format. There are some essential features, however, that all maps should have. Before you proceed to format your map take a look at some of the essential map features of the Bedrock Map of Hubbard Brook Experimental Forest. To look at some other geologic maps, you can browse through the images at the USGS Maps on Demand site.

Laying out the Map

  1. To format the map we use the ArcView Layout Function. Go to the Project window, and highlight the Layouts icon, and click new.

  2. Under the Layout menu choose page setup, and change the orientation of the page to landscape. Click OK.

  3. Add the Bedrock Map view to the layout, and choose a user-specified scale of 1:24,000.Unclick Live Link. This will prevent changes in the view page from affecting the Layout and will lock the map in as is. Click OK.

  4. We will want to add a "graticle" and grid to the map that specifies the latitude and longitude coordinates on the map. To do this we will need to add an extension to ArcView. Under the File menu, choose Extensions. Check the box next to the Graticles and Measured Grids extension. Click OK. You should see a new button added to the top of the layout page. If you draw the box that you use to insert the map into the layout too big, you will end up with whitespace between the gratcles and the edge of your map. Ideally, you want the Graticle/measurement grid to fit as closely as possible to the map, so click and drag on the black squares to resixe the box until it is the same size as your map. When you i nsert the Graticles, it should now fit very tigh with the edge of your map.

  5. Click on the graticle button, and choose to include both a grid and measured grid to the Bedrock Map view. Click Next. In the next dialog window choose a lat/long interval of 0 degrees, 0 minutes, and 30 seconds for both lat and long. Accept the defaults in the subsequent dialog pages and then click Finish to create the graticle.

  6. Next, add a legend to the map using the . You will see that the Legend text is in geologic symbols. To change this, delete the legend and open up the Bedrock Geology view. Double click on the Hydrology theme to show the theme properties dialog box. Double click on one of the symbols and select the fonts button . Change the text from the ESRI Geological Symbols to a standard font such as Helvetica. Close the diolog box, click apply on the theme properties box and insert a legend in the map layout.

  7. Now add the other essential map features that belong on a typical geologic map. Add all the 8 features listed, except for the Thumbnail map showing the location of the site. These features can be added by selecting options from these buttons on the layout menu . Use the Bedrock Map of the HBEF as a guide, but do not feel constrained to follow the exact layout. You will be graded on the completeness and clarity of the presentation. You should ask another student our the TA to look at your layout before you print it. It is difficult to proof read your own map, just like it is difficult to proof read your own writing.
  8. Print the map to the laster printer in the back of the room, by selecting Print... and then typing nsm858lw in the Printer box. Turn the map into your TA.
  9. You're DONE!