I have two line segments in an Adobe Illustrator file, line A and line B.

two lines that don't meet

I would like to find point C, the point where if line A were to continue down along its path and line B were to continue to the left, they would meet.

What is the best way to do that in Illustrator?


You can either use Smart Guides, dragging your anchor to-and-fro for a moment to get the "line extension" Smart guide to show up, or you can draw your own guides, snapping to the existing geometry; either approach works, and where some designers prefer one method, some designers prefer the other.

See screenshot below for smart guides line extension snapping:

enter image description here

Ctrl+5 with segments selected converts those selected segments into custom guides - see screenshot below for custom guides.

enter image description here

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  • In your Custom Guide example screenshot, it seems like just the two individual line segments of the square shapes have been turned into guides, but when I have a line segment selected and hit Ctrl-5, the entire shape that the line segment is a part of turns into a custom guide. In your example, were your line segments connected to the squares, or were the squares made of four individual, unconnected line segments? – Michael Davis Apr 6 '18 at 21:50
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    Neither: I wanted to emulate your condition in which you wanted to extend one vertice to an arbitrary intersection point, so I had two square-tool squares, carefully unaligned. I then drew a line (using snapping with smart guides) along one of those baselines which was supposed to intersect and declared it a Custom Guide (Cntrl-5) and then repeated this action on the other square. I did this so that it was a workflow mostly closely aligned with your question - something you can do once you have your initial figure(s) set up and realise you need to move a vert. – GerardFalla Apr 9 '18 at 15:19
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    Ah, that makes sense! Thank you for the clarification, and the original answer. – Michael Davis Apr 10 '18 at 16:51

You can use Transform Effect: select both paths and open menu Effect->Distort and Transform->Distort, set scale Horizontal and Vertical to some large value( in my example 400% will be enough):enter image description here

To return paths to normal state open Appearance Panel and delete Transform effect.

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  • When you say select both paths, do you mean select the two endpoints of each path? Also I don't have a "Distort" menu under the Effect menu, I have a "Distort and Transform" immediately under the Effect menu, so we might have a different version of Illustrator (I'm using the latest CC version). But, under that "Distort and Transform" menu I do have a "Transform" effect that matches the Transform Effect window in your screenshot. When I scale by a large amount, like 400%, it just scales my entire shape up to 400%. So I'm not sure if I'm doing something wrong but I don't entirely follow :) – Michael Davis Apr 6 '18 at 19:15
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    Yes, the right menu item: Effect->Distort and Transform->Distort. 'Select 2 paths' means select 2 separate paths (you can see it in a layer panel as a 2 separate items). Your qustion was about 2 separate paths (not a shape that consist of a single path), since if you have a shape this method just scale this single path. – emax Apr 6 '18 at 19:43
  • In hindsight, I should have said "two line segments". (If you look at the image in my original question, you can see it is indeed one 'path', I should have been more clear). – Michael Davis Apr 6 '18 at 20:10
  • I have edited the question to be more clear. Thanks for your answer! – Michael Davis Apr 6 '18 at 20:42

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