Repeating a line at a set distance is a common cartographic requirement. Especially when it comes to creating map sheet marginalia.
When creating a paper map sheet, I generally prepare as much of the map as possible in a GIS. Whilst publication direct from GIS is much improved, many cartographers prefer the freedom and expansion of options that come through finishing in Illustrator.
So if one considers the map border, with the graticules and scale or decorative patterning; I would usually create my ‘page’ to size and scale in a GIS along with the map frame, grid and associated values; then export as a PDF. But your starting point could equally be manually created straight in Illustrator if you know the exact georeferenced proportions of your page.
Opening the PDF as my working file ensured an artboard of the correct size with all the key information in the right georeferenced location on the page.
You’ll notice my grid is longitude and latitude rather than British National Grid, this is because I was replicating the earliest Ordnance Survey maps which were pre-BNG, but the principle is the same. For the scale of my map I decided to show every 1 degree as a main bar and break this down into a sub-scale of smaller bars.
I also showed bars for the real-world distance units with a tick or marker line every 1 furlong with half-furlong bars between.
Using each of the above I will show you three different techniques for creating an accurate repeating bar or line pattern.
Method 1 – Copy, paste and align
Copying and pasting may not sound like a reasonable option but it depends how many lines you need to draw, and there are certain ways of making it less laboursome.
For repeating a handful of lines you can use the Move function. On my map scale, 2 inches to the mile, 1 furlong is represented by 6.35mm. If I wish to repeat a line every 6.35mm I can draw and select my first line, then use Object > Transform > Move. Enter my distance of 6.35mm and click Copy.
For more lines you could create 4 or 5, make a group and then use Move and Copy. However for the number of furlongs on my map this would still not be very practical.
Another approach would be to calculate the number of lines you need.
Say I need 16 lines. I can draw the first and last lines as below.
Then, in the layers panel, select either line and copy (Ctrl + C) and paste in place (Shift + Ctrl + V) until you have 16 lines. Again you could copy and paste to create say 4 lines, then select all 4 and copy this 4 times.
Then, assuming the first and last line are the required distance apart (for 16 units), you can select all 16 lines, and use the distribute tool to separate them equally. Go to Window > Align and select either Horizontal Distribute Centre (in the case above) or Vertical Distribute Centre if you’re doing the side margins.
Not the most efficient method but it is quick and easy if you don’t have too many lines and is definitely better than placing lines one at a time.
Method 2 – Blend
To create the regularly spaced lines we simply need to place one at either end of the sequence
So here, on my map, I have placed two lines (shown in red for clarity) that are 16 furlongs apart based on my map scale. These will be my repeating element.
I want to show a line every furlong.
I could have used the previous method, but it is quicker to simply select the lines at either end, then click on Object > Blend > Blend Options.
You can experiment with different amounts of steps, but here I will use a specified distance of 6.35mm.
I am using 6.35mm because this is the distance at a scale of 1:31 680 (my map scale of 2inches to 1 mile) that represents 1 furlong in ground units.
Click OK, then go to Object > Blend > Make to apply the blend.
You can see I now have 16 lines, each 1 furlong apart.
To create the bars on the mid-points, I create a new line in between one of the furlong markers as shown below.
You will also notice I have been able to restyle my previous blend. Go to Object > Blend > Expand and it will become a group, Object > Ungroup will give you 16 independent line features.
To find the half-furlong midpoint, select the new line and the ones either side and from the Align tools (Window > Align) choose Horizontal Distribute Center.
Select only the half-furlong bar and copy (Edit > Copy) and paste in front (Edit > Paste in Front). Move this by changing the X value in the Transform panel, in my instance adding 15 lots of 6.35mm (95.25mm) to the value.
Select both bars, and select Object > Blend > Make (note the option will still be set to a specified distance of 6.35mm).
This new blend can be expanded and ungrouped and restyled as before. And there we have it, a furlong marker pattern around the frame of my map.
Method 3 – Rectangular grid
When you have boxes or numerous repeating lines, you may find the rectangular grid tool to be of more use.
Here I have 58 lines in each (alternate) ‘box’ of my pattern.
To create one such box, we don’t really want to have to draw 58 lines, even by a copy and paste method. So instead we can use a tool.
If you don’t have it already open, go to Window > Tools to open the tools panel.
Find the Line Segment Tool, left mouse click and hold on the tool. You’ll see some more tools available.
From these choose the Rectangular Grid Tool.
Now double-click on the tool in the panel and it will open an options dialogue. Here we can set how many dividing lines we want. And the default size, but this is basically optional as you can drag the box to resize.
So for 58 vertical lines as a box, I want to use the outside rectangle as a frame, insert 0 horizontal dividers, and 56 vertical dividers.
Click OK and then click and drag to use the tool. You can see that it will place our framed vertical lines with 58 lines from end to end.
However if we know the exact size the box should be, we can enter that into the options. On my map, every 1 degree of longitude is represented by 36.432mm. So this is our box width. And the height I want is to fit with the other lines of my marginalia and is 2.11mm.
So, I return to the options by double-clicking on the rectangular grid tool. Enter the values as above (shown below):
Click OK to accept. Now click on your page once (with the tool still selected) and you’ll generate a box exactly how you wish it to be sized and arranged.
Now you could repeat this using method 1, with or without drawing the alternating empty box.
But what I did was use method 2. So place one box at the start and another at the end of where we want the repeating boxes to be. Note that for size I am only showing (below) a section of my margin. In reality I would have far more boxes.
Select both boxes (they are groups) and go to Object > Blend > Blend Options. Set the specified distance (or steps), in my case 2 x 36.432mm (as it is alternating), which equals 72.864mm. Illustrator will round it to 72.86 but 2 decimal places is close enough.
Click OK and then choose Object > Blend > Make. We now have our repeating pattern.
I also used this method to create building hatching but unfortunately due to its size and complexity it would not export properly after clipping — see later Photoshop tutorial for more.
Combining all of the above, I was able to create the sheet margins for the old-style map of London.
Finally, you may have noticed on my early 19th century style map of London that recently went on sale at os.uk/maps that my lines are slightly crooked. This was done on purpose to replicate the askew lines of the original maps. This was easily achieved in Illustrator by applying a filter. Select your linework and go to Effect > Distort & Transform > Roughen.. Use the settings preview to find what works for you. Mine were set to Size: 2% Relative, Detail: 2/in and Corner.
You can see the effect in the image above.