When writing a flow chart, I can understand that it is a best practice to generally read left-to-right or right-to-left per locale, and/or top-to-bottom and generally for the directional flow of the chart to be consistent.
But, when it comes to a diamond ("decision") element and its yes/no or true/false result arrows, is there a convention as to which one ought to be pointing down and which one to the side?
Yes, there is such a convention, but it is not based on true or false. The "happy flow" will always be pointing down and any exceptional or side-tracked flow will be pointing left/right.
E.g. if you have a decision based on whether you are having to set up a new client or use an existing client, the existing client is the nice direction ==> go down.
The standard is old, but was required learning back when programming required flowcharting your solution, as you would get precious little time interacting with the computer (if you actually touched it at all).
https://fulmanski.pl/zajecia/wdi/zajecia_20142015/materialy/IBM-FlowchartingTechniques-GC20-8152-1.pdf indicates that the default directions for flowcharts is "left to right" or "top to bottom" and directions other than those require arrows to clarify the direction.
This is likely due to the predominance of the English language in computing at the time, earlier Graphical Design rules have always indicated that in order to enhance clarity on information presented serially (one item should be read before another), "reading order" of the language should be followed.
No, there is no such convention. I have even seen flowcharts where both the yes and no (or true and false) arrows attached to the side of a decision element.
It all depends on how you can best get the idea across that you are showing in the diagram.
