How to extract data points from a scatter plot
A scatter plot hides its table in plain sight: every marker is a row. Here is how to get the rows back.
Steps
- Drop in the plot (PDF if you have it).
- Each series comes back under its legend name, one row per marker.
- Check the rings: a marker with no ring was missed, and a ring on empty paper is a value to remove.
Markers that overlap
From a PDF, overlapping markers are still separate shapes, so every one is read.
From a picture, markers hidden under others cannot be seen by anyone. The result tells you when marks in the picture are not accounted for.
Log axes and error bars
Log axes are read as log axes. Error bars are read as the values at their two ends, in their own columns.
Questions
How many points can it read?
Hundreds per chart. Very dense clouds in a small picture are better read from the PDF.