GIS Blog

Of Graticules and Grids

In this post we look at adding grids and graticules to maps

I hope it’s not too much of an exaggeration to say that most people who like GIS also love maps.  I mean love maps.  Okay, at least I do.  With the tramping renaissance going on in my whanau, that has gotten us focused on NZ’s 1:50,000 scale topo maps that most trampers would (should!) take along with them when going bush.  They are as essential as water and a PLB, as far as I’m concerned.

(Notice how the blue grid is helpful for estimating distances – each square is 1 km x 1 km)

While I do love those maps, on a recent tramp I found myself getting a bit frustrated whenever I wanted to have a quick peek.  It usually meant stopping, taking off my pack, taking out the map, unfolding it, having a look and then doing the reverse.  On a recent walk to Angelus Hut in the Nelson Lakes National Park, I thought I’d be clever (Ed. never a good idea) and print out some of my own maps using the LINZ topo basemap available in Pro.  Printed out on A4 sheets, these mini-maps would be easier to pass around and refer to quickly while also fitting easily in a pocket.

So, to get things started, I opened a map with the basemap set to the NZ LINZ Topographic option:

I then set the extent to what I wanted on the map and sent this to a new Layout (Insert > New Layout), choosing A4 Landscape.  I decided to do two maps, one for each leg.  Day 1 was the Cascade Saddle track:

(Note: we cheated a little bit…we took a water taxi from St Arnaud to Coldwater Hut.  Very much appreciated that at the end of the Cascade Track!)

As usual, I ended up a bit of rush so quickly printed out this map and its Robert Ridge companion before heading away.  I didn’t bother with legends and north arrows because I knew the blue gridlines would help with orientation and estimating distances.

Imagine my surprise and disappointment when I first opened the map and realised that there were no blue gridlines!  That’s right – I hadn’t noticed it in my haste, but the Topo basemap in Pro doesn’t include them.  Ah well, not the end of the world, just a bit frustrating. I vowed to do better next time around.

And the next time around came quickly – the Nydia Track in Te Hoiere/Pelorus Sound:

I decided to break these into four maps – one for each leg, the first being from Kaiuma Bay to Kaiuma Saddle – given the N-S nature of the track here, I switched the orientation to Portrait:

Notice that I still don’t have my blue grid lines.  Not to worry, I can easily add them.  With the layout window active, I’ve got a Grid option on the Insert tab:

Under that, I’ve got a choice of either graticules or measured grids:

What’s the difference?  Graticules specifically use latitude and longitude coordinates while measured grids use projected coordinates (e.g. metres, nautical miles, cubits).  In this case I’m interested in using metres, so I’ll go with the option of Blue Vertical Label Grid to match the topo maps – just select in the window, et voila!

Still a bit of tweaking to do.  It’s not essential (for me) that I have the measured values for each line (might be if I were wanting to use GPS to map my position) so I’d like to turn them off.  I’d also like to ensure that each square is 1 km x 1 km as they are currently 500 m x 500 m.  I’ve got my Map Grid Options pane open:

Note that it’s picked up the coordinate system (NZTM) from the data themselves.  Not much I can do here to change things, but switching over to the Components gives me a bit more control:

Here I could remove the Labels (and the Ticks, too, they’re a little annoying without the labels) and reset the Interval to my desired spacing:

A VERY IMPORTANT POINT: Before I could reset the Interval I had to go back to the Options pane and untick the Interval > “Automatically adjust” box.

With all that in place, I think I’ve got what I need to print out my handy trail maps:

While we’re here, it might be worth noting some of the other options under Grids, specifically Reference Grids and MGRS Grids ()plus the option to add our own):

Reference Grids allow us to use letter and number combinations to guide people to certain areas (e.g. Kaiuma Saddle is in cell B1).  My map looks like this with one:

 

Hmmmm….bit too much, methinks.  MGRS is a Military Grid Reference System – a specific measured grid that makes use of the UTM global coordinate system, the Universal Transverse Mercator system (Ed. man, that Mercator guy got around.):

It doesn’t make the map look that different apart from the lines being a bit slanted – there’s a longish story behind why that is which I’ll have to save for another day.

So if nothing else, we’ve got to see how we can add grids and graticules to our maps if they help our reader. I’ll be honest, I’m not a huge fan of adding grids or graticules to maps, except in cases like this. Here, the grid serves the purpose of allowing a quick estimate of distance as well as orientation, which can be important on the track.  But often, adding a grid to a more general purpose map ends up not really adding much. Choose wisely, young Jedi: just because you can doesn’t always mean you should.

C.

• 26/07/2022


Previous Post

Next Post

Leave a Reply

Your email address will not be published / Required fields are marked *