You can use translate to shift the coordinate system. Just shift it the opposite direction, for example:
ctx.translate(-500, -1200);
Now when you draw something at 583, 1642 it will show up at 83, 442 relative to the view-port.
To reset just transform back or initialize with an identity matrix:
ctx.setTransform(1, 0, 0, 1, 0, 0);