You'll of course need inkscape installed

You'll need an image. .png's work, probably other formats too. It should be as straight as possible. Use a tool like the Gimp to correct rotation if necessary. It should be straight enough so that a line from top/bottom or left/right is straight enough for your purposes.

This assumes that you have a 90 degree routed sample. You'll have to make tweaks but nothing major for something not of that nature.

I am as of the time of this writing us a mix of Inkscape 0.47 and 0.48.

Launch Inkscape and lets get started

Edit ⇒ Preferences

• Pen: Create new objects with: Last used style
• Shapes: Rectangle: Create new objects with: Last used style

Without this every time you create a new polygon you'll have to keep re-selecting things.

And save it somewhere.

File ⇒ Document Preferences

• Grids: Spacing X: 1.0000
• Grids: Spacing Y: 1.0000

• Snap: Snap to grids: Always snap

Without this it will be difficult to get polygons to line up predictably.

Create a new layer to store the image.

: I forget how to do this nicely

As a workaround save and close. Open up a text editor and find the layer you just inserted. Make it look something like this:

<g
   inkscape:groupmode="layer"
   id="layer2"
   inkscape:label="background"
   style="display:inline"
   sodipodi:insensitive="true">
  <image
     sodipodi:insensitive="true"
     y="0"
     x="0"
     id="image12"
     height="9295"
     width="9515"
     xlink:href="stitch.png"
     sodipodi:absref="stitch.png" />
</g>

Save and re-open the document. You should now be able to show/hide that image as a layer. I suggest also locking it so that you don't move it around.

Select the pen tool (“Draw Bezier curves and straight lines). This toolbar is by default on the left.

Select the “Use straight lines” box at the top.