How to draw a map with a pen plotter
A map is one of the most rewarding drawings for a plotter: thousands of strokes, no fills and a result nobody mistakes for a print. This guide walks through the whole process, from file to finished sheet.
What a pen plotter is, and why maps
A pen plotter is a machine that moves a real pen over paper, following strokes. It does not print dots like a printer: it draws lines, just as a very precise hand would. There are commercial ones (like the AxiDraw) and many home-made ones, often built from a 3D printer.
Maps are a perfect fit: they are made of lines (streets, rivers, contours), their density can be controlled with the scale, and the result, with the ink slightly raised and the small variations of the pen, has the feel of an old engraving.
The one condition is that the drawing is made of strokes only. An ordinary map SVG has areas filled with colour and lettering as outlines: the plotter would draw just the edges and you would get an odd skeleton. That is why the file has to be designed for plotting from the start.
Preparing the map
In PlotMyMap everything drawn is a stroke: parks and water are filled with hatching, the sea with shore lines, and text is written in single-stroke lettering (Hershey fonts), so there is nothing the pen cannot do.
Pick the real paper you will use and its margin first, then the scale. Mind the density: a city map at 1:25,000 can have tens of thousands of strokes and take hours to draw. To begin with, an A5 or A4 of a village or a neighbourhood at 1:5,000 or 1:10,000 is a good first project.
Enter the line width of your pens. It is used to compute the hatch spacing and the margin it keeps from outlines, so the ink does not smudge the edges. With a 0.3 mm fineliner and the width set to 0.3, hatching stays clean.
Download the SVG. It comes out true to size in millimetres, with one layer per colour (and per width) that Inkscape and vpype recognise, and with strokes already merged and sorted to save pen lifts.
Optimising with vpype
vpype is a free command-line tool that is almost standard in the plotter world. It is not essential with an SVG that is already prepared, but it helps to check and tweak the file before drawing.
A typical command: vpype read map.svg linemerge linesort reloop linesimplify write ready.svg. linemerge joins strokes whose ends meet, linesort orders them so the pen travels as little as possible in the air, reloop picks the best starting point of closed lines and linesimplify removes points that add nothing.
With vpype read map.svg stat you will see how many strokes each layer has and how many metres of ink the pen will travel. It is the best way to estimate how long the drawing will take before you start.
Do not scale the drawing in vpype if you want to keep the map's scale: the SVG already has the paper size.
Pens and paper
For most maps, technical fineliners from 0.1 to 0.5 mm give even lines and do not dry out quickly. For fine detail, 0.1 or 0.2 mm; for the title and main roads, 0.5 mm or more.
Gel pens give very bright colours and work well on dark paper, but they blot more if the pen pauses on a spot. Pigment inks resist light and water: the best choice if the drawing will end up framed.
The paper must be smooth and fairly heavy: Bristol board, 200 g/m² or heavier drawing card, or marker paper. Textured watercolour paper makes the line skip. Tape it firmly to the bed with painter's tape at all four corners: if it moves a millimetre mid-drawing, the colours will no longer line up.
Layer order
Each SVG layer is a colour, and the usual approach is to draw them one by one, changing the pen in between. Order matters: light colours and fills first (water, greens, background hatching), then structure (streets, buildings, contours) and text and frame last, which must sit on top and stay crisp.
If a layer passes over another whose ink is still wet, it can drag it. Leave a few minutes between colours, especially with gel.
The map colours on screen are a guide for splitting layers, not the exact ink. You can give each layer the closest pen you have, or draw everything in black: a monochrome line map looks wonderfully elegant.
Speed, pressure and tests
Going slowly gives more even lines, especially with fine tips. A good starting point is to draw slower than the machine allows and raise the speed once the line stops failing.
Pressure should be just enough for the tip to touch the paper: press harder and the tip splays and the line thickens. Many plotters let you set the pen height; it is worth fine-tuning on a test sheet.
Before launching a three-hour drawing, do a small test: the same map on A6, or a single layer. You will find out in time whether the pen skips, the hatching is too tight or the paper is not held well.
Common problems
Lines that do not close or shifted colours: the paper has moved or the machine has lost steps. Hold the paper better and lower the speed or acceleration.
Blots at the start of each stroke: the tip rests too long on the paper after lowering. Shorten the delay after pen-down or use an ink that bleeds less.
Hatching that turns into a blob: the spacing is smaller than your pen's real width. Enter the right width on the map or widen that element's spacing.
A never-ending drawing: too much detail for the paper. Zoom the scale out, drop layers that add nothing (minor streets, buildings on a mountain map) or pick a smaller paper. PlotMyMap does not produce G-code or control any machine: the SVG goes through your usual software (vpype, Inkscape, your plotter's program).
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