How to plot a logarithmic graph with 2 y-axis?

[kureoshin]

Hi,

I have to plot a logarithmic graph for the crater density on Mars. I have the data for crater size range for x-axis, and the number of craters on the y-axis. I was told to create a crater density plot using the data and to extrapolate the age of the surface of Mars based on the intercept on the secondary y-axis. I am stuck as to how to create the graph.

My instruction were to plot the points so that the number of craters were on the y-axis and the size of the craters were on the x-axis. But, I don't understand how they got the graph to plot 6 different lines where neither of the lines intersect the x-axis at all for that matter. One of the lines is a best fit line so there are 7 lines in total to plot. I know that the primary y-axis is logarithmic and I think the secondary y-axis is logarithmic too.

I have attached a PDF showing how the graph should look like. Any help is appreciated.

Crater stuff pg 3 only.pdf

Edit: I think all the axis are in a logarithmic scale. The x-axis is suppose to be in kilometers, but if I extend the graph to the left the x-axis would be smaller. Apparently, before 2 kilometers, I can label the axis in terms of meters so a full graph would have the values go from 0, 16, 32, 64 m... until 1 km, 2, 4, 8, ...128 km on the x-axis.

[MrShorty]

A few observations.

I can't tell what they are doing with the x axis, either. It kind of looks like a logarithmic axis, because the integer powers of 2 (2, 4, 8, 16,...) are equally spaced. However, if the axis were truly logarithmic, the axis mark for 3 would be closer to 4 than 2 [log(3,2)=1.6 not 1.5]. Perhaps they are not worried about the exact placement of the non-integer powers of 2.

I think you are misinterpreting the graph in terms of the secondary y axis. I don't think that the surface age number are for an axis. Rather, they appear to me to be "curve" labels for each of the "contours" plotted. I can't say for sure what is going on "between" these contours (the space between the 2 and 3 by curves is much smaller than the space between the 3 and 4 by curves), it is probably something empirical.
At this point, how much of your question is planetary geology, and how much of it is related to Excel?

As far as Excel goes, plotting a contour plot like this is normally fairly straightforward. Enter the data in the spreadsheet. Contour plots are usually easiest to generate from a table that looks like:

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Then select this table and insert a scatter chart, then format the chart as desired. (Help file with basic steps for creating scatter charts https://support.office.com/en-us/art...5-104A9018B86E )

Plotting the results of the table at the top should also be straightforward, once you decide what xvalue should be assigned to each range (should the 8-16 category be plotted at 8, 12, or 16?).