Tutorial: Create a Histogram Plot of a Single Variable

Estimated time: 2 minutes.

A frequency histogram is a graph that displays the distribution of real number values, read from a single datasheet column, by percent or actual occurrences.

! It is assumed that you have opened the "Maps_Surface_Geochemistry.RwDat" data file as discussed in the previous lesson.

1. Click on the Utilities | Stats menu, and choose the Histogram option.
   
2. Data Column: Click on the down-arrow button on this prompt, in the left pane of the window, and select from the list of column names the Gold column to be analyzed. You may need to scroll upwards to see this column name.
   
3. Annotation: Click this tab.
   1. Plot Statistics: Check this box.
      1. Click on the font button next to it and set the Size to 2.0 and the text color to your choice.
      2. Verbose: Check this option.
         
   2.  Plot X-Axis Labels: Check this setting.
      
   3. Plot Y-Axis Labels: Check this option.
      1. Plot as Percentages: Un-check this box. This tells the program to plot actual occurrences rather than percent.
         
4. Scaling + Bin Size: Click this tab.
   1. Linear: Click in this radio button.
      • Automatic: Choose this linear scaling option. This will set the bins to 1/10th the standard deviation. In your own work, if you prefer to declare the actual number of units for each bin, you can select the Manual option.
5. Bin Colors: Click this tab to select how the diagram will be colored.
   1. Discrete: Choose this option. This will apply different colors to the bars in the graph based on their relationship to the mean and standard deviation. You can view/adjust the default colors.
      
6. Click on the Filter tab and be sure both options are turned OFF.
   
7. Legend: Unchecked
   
8. Aspect Ratio: Click this tab and be sure Fixed Width:Height Ratio is off
   
9. Other 2D Files: Unchecked
   
10. Peripherals: Check this box and click the tab.
    1. Title: Check this option to activate the diagram titles:
       1. Primary Title: Type: Gold
       2. Secondary Title: Enter: Surface GeoChem Data Set
    2. The other Peripherals items can be unchecked.
       
11. Border: Unchecked
    
12. Click Continue to proceed.

    RockWork will build the frequency histogram and display it in a new RockPlot2D window on the screen. RockPlot2D is the plotting program for maps, logs, and other 2D diagrams.

    For this type of geochemistry data, the values of interest lie in the Slightly Anomalous and Anomalous groupings, particularly the latter, beyond the mean plus 2 standard deviations.

13. Look closely at this group. This plot shows four samples with anomalous (high) gold values.

    

    Let's take a look at where these samples lie; the next tutorial lesson teaches you how to build a proportional symbol map, in which those sites with larger gold values are plotted with larger symbols.

14. If you wish to save this plot, choose File | Save from the RockPlot menu, enter a name such as: Gold Histogram   and click Save.
    
15. Close this window (X).
    

  Frequency Histograms

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