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Tutorial: How To Design a Transit Diagram

One thing I often get asked regarding my transit diagrams is how I go about actually creating them. Originally, I just jumped right in and pushed things around on a page in Illustrator until it looked okay. These days, I’m far more organised, meticulous and precise with my work and I think it shows in the quality of my diagrams. Here’s a few tips and tricks that I live by when working on them:

Plan Before You Start.

Take time to consider everything about your diagram. How thick do you want the route lines to be? Are they touching, or is there a slight gap between them? Are you going to use curves or straight edges where a line changes direction? Consider your station markers – will they be ticks, dots or something else? Think about how you would like to differentiate interchange stations or transit centres as well. Consider the typeface you’re going to use for station names – it should be legible and simple. When you’ve considered all these points, you’ve given yourself a set of rules that you will use to construct the diagram. Every design decision you make should be evaluated against these rules: sometimes, you can break them if needed, but it definitely helps to have them in your head as you work.

Look at an actual map of the area you’re converting into a diagram. Draw rough route lines onto it if needed. Look to simplify the routes down to their essential elements: horizontal, vertical and 45-degree angles. Identify the most complex interchanges as they almost always need the most work. Solve them first, and the rest of the diagram often builds itself. Look for interesting compositional shapes or strong vertical or horizontal axes to build your design off. Some diagrams incorporate geographical idiosyncrasies as an identifying part of the diagram, such the DC Metro diagram’s retention of the “jog” along the western Red Line between Tenleytown and Van Ness.

Use the Right Software.

Creating a transit diagram is a very precise task, with route lines and curves that need to match up with each other perfectly to look right, an underlying grid that holds the diagram together and professional-looking typography for station names and legend. For this kind of work, you must use a vector graphics editor like Adobe Illustrator, CorelDraw or Inkscape. When I see diagrams done in Photoshop or MS Paint, I wonder how the creator even started the project, let alone finish it!

Define Your Grid.

From experience, I’ve determined that the most useful grid to have is one that equals the distance between the centre lines of two adjoining route lines. This equals the thickness of those lines if they are touching each other, but if you want a bit of a gap between your lines, then this isn’t true. So, if you have 12-point lines that touch, use a 12-point grid. If you have 10-point lines with a 2-point gap between them, then you’d also use a 12-point grid. I often leave the lines at the full thickness of the grid while I work to ensure everything is lining up right, then make them thinner as required at the end.

Carry the grid through to other elements in your design: use a multiple of it to space your stations evenly along a route. If you have a 12-point grid, you might space stations 48 or 60 points apart. If you want to have curves instead of angled lines where a route changes direction, you may want to set them up as a multiple of the grid as well, although this can often be an aesthetic decision. The bigger the radius of the curve, the more elegant your diagram can look.

Let the Software do the Work for You…

Try to do as little manual placing or editing of your routes as possible. Snap paths to the grid to ensure precise placement. Use numerical values for transformation and movement functions as much as possible, especially when you’re moving things at angles other than right angles, as lines may not conform exactly to the grid in these situations. I love using Illustrator’s Smart Grid (Cmd/Ctrl-U) overlays when working on my diagrams, as it shows me when paths snap to points and angles.

…Except When Doing it Manually Works Better.

One thing that Illustrator can’t help you with is adding curves to route lines. You might think that the “Round Corners” effect would be perfect for this task, but it simply doesn’t work. It can do 90-degree corners well enough, but its algorithm doesn’t work as well with 45-degree curves: if you have two or more route lines going around a corner together, they don’t line up with each other at all.

What I do is create a set of master curves that I then manually cut and paste into place once I’ve laid out the overall design of the diagram. Draw as many concentric circles as you need – if your diagram has a curve where five routes change direction together, then you’ll need five circles – then cut each circle into four sets of 90-degree curves. Repeat, except this time, cut your circles into eight sets of 45-degree curves. Keep these master curves off to the side and use them as required. Copy the curves you require, place them precisely over the corner you’re working on (having those Smart Guides on works really well here), cut out the straight lines underneath your new curves and delete them, then join the curves with the remaining segments of the route lines. Time consuming, but absolutely the most accurate way to add curves.

Note: this part of the tutorial is no longer true for users of Adobe Illustrator CC and above, as Adobe has integrated the excellent “Live Corners” tool into the program. See this post on the Transit Maps blog for more information.

Consider Typography as an Integral Part of the Design.

Labelling of stations is one of the most difficult parts of creating a transit diagram. Whatever you do, don’t leave it until the end. Ensure your design has enough space so that type isn’t crammed into an inappropriate space.

Erik Spiekermann once told me – in typically forthright manner – that “a designer who cannot make all the type horizontal is a loser”, and I’m definitely inclined to agree with him. Labels that are set in entirely horizontal type are far easier to read. You can alternate station names above and below a horizontal route line to save space. If you must angle your type, try and do it from one direction only to minimise the amount of head turning that people have to do. Having your type read from the right (tilting the head to the left) is preferred.

Use Layers.

I can’t stress this enough. Each route line should be on its own layer. Stations should be on their own layer. Text should be on its own layer. Any geography should be on its own layer. You can thank me later.

Use Global Colours.

I don’t understand why Illustrator even lets you make non-global colours. This is such a useful feature to quickly tweak the look of your diagram. Want your Red Line to become a Green Line? Use global colours and simply edit the swatch: that colour changes everywhere in the document.

That’s it! If you have any questions or comments on these tips, let me know about it.

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    • That’s a whole other kettle of fish — first you have to acquire or create that accurate background map! You can draw it yourself in Illustrator (better if you want to stylise the content at all), or get it from a GIS or OpenStreetMap (better if you want truly accurate street paths)… all of which takes time and considerable effort and skill. And then you have to overlay the required information in a clear, easy-to-understand manner — which is probably the hardest part!

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  3. Martin Glavalo

    Thanks for your generosity in sharing these valuable lessons. As a recent AutoCad to Illustrator convert, the rounded corners have been a baffling mystery to me…until now. Thanks for the clarification and work-around. Now I can stop looking for the FILLET command in Illustrator.

  4. Jeff Bridgman

    Thanks for the valuable insight! I’m working on a map of Tokyo (quite an undertaking….) and the global colors and grid use are something I never thought of using before…. it might be a bit too late now, but I’ll definitely incorporate those in the future! 🙂

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  6. It’s always interesting and enjoyable to see how others work, it’s very considerate of you to describe your workflow. Especially when you could feel there’s a danger of disclosing the secrets for your success, but that’s obviously not the case.

    I feel there’s one small error though. Round Corners does work with every kind of angle, there’s just a mathematical detail with cornering parallel lines; an outer curve naturally has a larger radius, but Round Corners asks only for a single value.

    I drew an illustration of what I think you mentioned versus what I do (I hope it’s not too messy, I added guides if this helps others too):

    The left group clearly has identical radii, because the same radius was multiplied. If you Expand Appearance before that, offsetting handles the radius correctly.

    You will lose the ability to edit the radius later when expanding the path, so another approach would be to calculate the radius for every subway line separately, a value which is dictated by the grid, then rounding the corner.

    But you are correct; doing manual time-consuming work will get the best results. And nothing feels better than that.

    • Chris,

      an interesting and thorough post – but it doesn’t address the fact that Illustrator’s implementation of Round Corners is fatally flawed when it comes to consistent results. Read my response here:

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  8. Olivier

    Thats a lot of good advice, thanks 🙂
    One software that’d work very well for this is Autocad. It’s very easy to link 2 straights with a curve, to work with layers, to create for example a “station” item that lets you change its look throughout the whole map at once, create typeface styles that let you change your typeface or its size on the whole map at once, etc.
    For those who have Autocad i think it’s the easiest software for that kind of maps 🙂

    • Jeff Bridgman

      AutoCad is definitely helpful. For example, if you have two arcs of a certain radius and need to draw a line tangential to them both, no problem! Doing the same thing in a vector graphics program would probably require some math 😉

  9. As a (former) professional cartographer, all I can say is perfect ‘lesson’ Cam!
    Especially like your bits about grids and layers – I now work in the world of graphic design and magazine layout, but still separate everything into layers. I think I’m in a definite minority amongst designers for that, and it frustrates me whenever I have to edit other designers’ files!

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