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Lab 03 - Reproducing Maps - Geologic Map

 

Background

Cartography, the art of making quality maps, is widely claimed to be a dying art. In the age of smart-phones, tablets, and ubiquitous broadband Internet, modern consumers expect on-demand, instantly and infinitely scalable maps with current spatial data, high-resolution imagery, and a soothing voice to tell them how to get where they want to go. To satisfy this demand, mapping services have all but abandoned traditional maps in favor of GIS-based web applications designed to provide a user-friendly interface with selectable layers.

In many cases, these applications provide more information with more clarity than old paper maps ever could (although users would do well to remember that most "free" online mapping applications make money by both feeding consumers tailored advertising recommendations and selling consumers' information back to advertisers). In other cases, these applications are complicated, cumbersome, incomprehensible, and/or incomplete.

Very few 21st century consumers express interest interest in traditional paper maps, and there is consequently little demand for cartographers. Professional cartographers, those with the skills and experience to make effective, readable, and attractive maps, are a dying breed. Those who depend on (or at least prefer) paper maps will be greatly impacted if this happens, but most consumers likely see no reason to preserve cartography as an art or profession. However, if we lose the ability to make a quality map on paper, how long until we lose the ability to make a quality map on a computer screen?

Lab 3 is an exercise in cartography, reproducing a portion of a geologic map in Northern Utah. After the map is created, some rudimentary area calculations will be run to determine major rock types.

 

Geologic Map Reproduction

The Utah Geological Survey offers printable maps and GIS data online, primarily broken into 30' x 60' quadrangles. At a scale of 1:100,000, the paper map for the Logan quadrangle is 36 x 26 inches (91 x 66 cm). This is too large for standard printers and too cumbersome for efficient field use. Reducing the scale to fit the entire quadrangle on a standard sheet of paper would reduce the resolution and utility of the data. Assuming the user knows his or her specific area of interest, the best solution is to retain the large scale but cut the unnecessary areas to get a manageable map.

In this exercise, the area of interest is Logan Canyon. Using the original map created by J.H. Dover as a design template, an excerpt of this map was reproduced to fit on a standard 8.5 x 11 inch (21 x 28 cm) sheet of paper at a 1:100,000 scale, as shown below.

A Portion of Geologic Map of the Logan 30' x 60' Quadrangle, Cache County, Utah
The pertinent GIS layers were imported into ArcGIS 10.2, and manipulated to closely match the design of the original map. For spatial reference, Lat/Long and UTM tick marks were added to the edges. Appropriate marginal information was included to complete the map. The map can be viewed on a computer, or printed on any standard printer (preferably color) and taken into the field. Click here to download a PDF of this map.

 

Major Rock Calculations

After producing the map, the second task was to determine which major rock units comprised at least five (5) percent of the excerpted area. Using the 'dissolve' tool in ArcGIS, the polygons of each rock type were consolidated the the 'geologic_units' layer. In the attributes table, fields were added for the area and percentage of each rock type. The area for each rock type was calculated, then calculated again to determine its percentage of the total map area (314.52 km2 - calculated from the clipped layer used to create the map). Each rock unit comprising more than five (5) percent of the total was selected and exported to a text document.

 
Rock Type Area (km2 ) Percentage
Beirdneau Formation 24.53 7.8
Hyrum Dolomite 20.1 6.39
Laketown Dolomite 28.8 9.16
Little Flat Formation 30.49 9.7
Lodgepole Limestone 18.42 5.86
Provo Formation 60.25 19.16
Other Rock Type 131.93 41.93

The text document was modified to include an 'other' category accounting for all other rock types (as shown in the table above), then multiple attempts were made to create a chart in ArcGIS highlighting the major rock types. Unfortunately, after three consecutive computer crashes this effort was abandoned. The exact cause of the crashes could not be determined but is assessed to be one or more of the following three issues:

  1. Glitch resulting from manual edits in the text file
  2. Luddite using Windows XP, an obsolete Operating System in 2014
  3. ArcGIS is an evil program which takes pleasure in preying on innocent users

The chart below was created without difficulty in Microsoft Excel, with the colors manually matched to those in the map.

Major Rock Types > 5%

Click here to download an Excel spreadsheet with this chart.

 

Expanded Legend with Rock Chart

 

One limitation of the reproduced map is that the legend only reflects abbreviations of the rock types, forcing users to refer to the original map for full names and descriptions. This is partly because of size limitations on the page, and partly because of the way the GIS layer files are designed and categorized. Using the 'field calculator' in ArcGIS, the geologic unit labels were combined to include the abbreviation and full name, but they lost the color scheme from the original map. When the original color scheme was re-imported, the original labels over-wrote the combined labels.

 
 

In order to create an expanded legend with the full rock names, some creativity was required (along with a little trial and error). Two layer files were created, one with the original colors and labels, and the other with ArcGIS default colors and the combined labels. The layer with combined labels was made 100% transparent. Next, identically formatted legends were created and stacked directly on top of each other in layout view. After ensuring rock types were sorted identically in both layers, the legend text for the original layer was made transparent. This produced the appearance of a single legend representing the original colors with the abbreviation and full name for each rock type.

 
 

The map below shows the expanded legend, the chart of major rock types, and a 1:200,000 scale map of the excerpted area. As a stand-alone, this map would not be very useful due to the small scale. However, as a companion to the 1:100,000 map it provides key complementary information. The aspiring geologist could place both sheets opposite each other in a letter-size document protector for quick reference in the field.

A Portion of Geologic Map of the Logan 30' x 60' Quadrangle, Cache County, Utah
 
Click here to download a PDF of this map.

References

Geologic Map of the Logan 30' x 60' quadrangle. GIS Map Data - Utah Geological Survey.

 

 

Ĉ
Kevin Turnblom,
Jan 29, 2014, 8:01 PM
Ċ
Kevin Turnblom,
Jan 29, 2014, 8:01 PM
Ċ
Kevin Turnblom,
Jan 29, 2014, 8:00 PM
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