What is the difference between Log and Linear when using a line chart

[emma313823]

Hi - 

I'm trying to understand the difference between log and linear when using the line chart visual.  I have a visual plotting revenue in the thousdands by month.  There are 3 lines on this chart...Actual which has data through September, Forecast Fixed and Forecast rolling which has numbers through December.  When I switch from Log to Linear - there is a dramatic differenct in the visual and am not sure which I should really be using.  Can someone explaine the difference and perhaps explain in what situation each is best used?

Emma

[v-qiuyu-msft]

Hi @emma313823,

In addition to @BhaveshPatel's suggestion, you can also take a look at this article: When Should I Use Logarithmic Scales in my Charts and Graphs?.

Best Regards,
Qiuyun Yu

[emma313823]

Thanks for this info...I'm still having difficulty understanding which one to use.  I have a dramatic difference in log to linear in this chart.  I've attached the chart in question.  Perhaps it is a scaling issue, which I'm having a great deal of trouble figuring out with the Y axis.  I'd like to set the bottom number at $250K and the top seems ok at $400K, but I can't figure out how I'm supposed to enter my numbers in order to achieve the correct scaled look.  We are using an outsourced web-service to do dashboards and they have indicated they are using a logarithmic option, which seems more in line with our forecast - being down against the forecasted numbers.  The gaps in the linear chart seem to really skew the visual.

Emma

[v-qiuyu-msft · Accepted solution]

Hi @emma313823,

From these two images, you can see the slope of lines are decided by the Y-axis scale. If you have data that is logarithmically proportional, you can consider using a log scale. This helps improve the appearance of the chart by making your data more manageable. For example, the field has data like this: 9, 102, 995, 1000. If not, it's better to use linear scale.

Best Regards,
Qiuyun Yu

[BhaveshPatel]

Hi Emma

There are two main reasons to use logarithmic scales in charts and graphs. The first is to respond to skewness towards large values; i.e., cases in which one or a few points are much larger than the bulk of the data.

Logarithmic scales can be useful when some of the data you are displaying is much less or much more than the rest of the data or when the percentage or ratio differences between values are important. 

A logarithmic scale in Report shows the base value of 10 raised to the power of a value. For example, 10 has a logarithm of 1 because 10 raised to the power of 1 is 10, 100 has a logarithm of 2 because 10 raised to the power of 2 is 100, and so on.