To position a connector on the PCB, I draw a line from the edge of the board to the desired location for the connector. This is the same method I use for positioning mounting holes. I then use the positioning tool to place the mounting hole at the exact point. How can I use the positioning tool to accurately place the connector?
When moving something you see in status bar current cursor position. Pressing Space bar you can also set start point for differential positioning also shown there (don’t have KiCad here to confirm it).
Don’t draw holes from scratch but use hole footprints. When you position such hole you see at status line its center position.
In KiCad V4 and V5 it was not possible to set absolute 0,0 into new position. Because of that since then I’m working around top left sheet corner. Thanks to that symmetric holes have symmetric coordinates.
You can see it here:
For THT connectors and other THT footprints I usually use a 2.54mm grid to keep as much compatibility with with matrix (vero) board as is practical. This is a grid that is so coarse that you do not need any sort of alignment tools. My PCB outline is always in rounded metric numbers (I don’t like banana units), and whole mm is also easy to do on a grid. I also try to incorporate (127, 127) as some sort of reference point on the PCB, most often pad 1 of a THT footprint. (127, 127) is a location that works with both a metric and that other grid system (It’s 5 bananas)
Using such a simple system mostly avoids most difficulties with measurements. But when it’s really needed, KiCad has a diversity of tools, from the positioning tools in the context menu, to directly typing in coordinates in either the properties of an object (footprint, line, circle, etc) or in the properties manager.
And you can also make use of geometry. You can for example create a (sketch) line with a certain length and angle, then snap one end of that line to your reference, and snap something else to the other endpoint. KiCad-Nightly now also has the capability to use intersections of graphic objects as snap points.