How to Use Great Circle Mapper Like a Pro

Great Circle Mapper, also known as “GCMap” and available at gcmap.com, has been a beloved tool among dedicated aviation geeks for as long as I can remember. However, it has recently been brought into much sharper focus by the revelation that Air Canada’s new Aeroplan will introduce a distance-based component into its new flight rewards structure.

Whereas there was never previously a pressing need for the average Canadian points collector to understand how Great Circle Mapper works (unless they were constructing a clever Avios multi-carrier award involving long and often uncomfortable flights), times have now changed, and it will soon be essential to familiarize yourself with this online mapping tool if you want to successfully extract value from the new Aeroplan.

In this installment to “Use It Like a Pro”, I’ll show you all of the Great Circle Mapper techniques that I use to plan my itineraries, chart out distances, and generate all the pretty routing maps you see here on Prince of Travel.

In This Post

1. Mapping a Flight

First, you’ll want to enter gcmap.com in your browser and pull up the Great Circle Mapper homepage. Here, you’ll find a rotating “Featured Map” that is usually pretty interesting to look at, but you’ll want to concentrate on the main input bar at the top, which is where the magic happens.

Let’s begin with the simple task of mapping a certain flight route and calculating the distance – to take one of the new Aeroplan’s sweet spots, let’s say Montreal–Lisbon–Casablanca.

You’d enter this in the form of IATA airport codes or city codes, separated by hyphens (“-“). So in our example, it’d be “YUL-LIS-CMN”, and press the “Map” button or the Enter key.

What’s that? You aren’t familiar with the world’s major three-letter airport codes off the top of your head? Sorry, I assumed everyone was.

If you don’t know the exact airport code, you can also enter the city name, and then Great Circle Mapper will ask you to “fix” a specific airport by choosing from a list of airports that match your entry, before showing you the finished map. However, it may be easier to simply Google “Casablanca Airport”, and you’ll find the airport code “CMN” pretty easily.

Either way, you’ll end up with the following output, which shows you a nice map of the routing, as well as the distances of each leg and the cumulative distance of the journey.

Let’s look up that figure of 3,645 miles against the new Aeroplan’s North America–Atlantic chart…

“0–4,000 miles”, 35,000 points in economy or 60,000 points in business, boom, done.

2. Mapping Multiple Flights

Now let’s take things up a few notches and map multiple routes at once. Use either a comma (“,”) or a semicolon (“;”) to separate different routes, and they’ll all show up on the same map:

If you’d like to map out multiple routes from the same origin to varying destinations, then you’d use a slash (“/“) to separate all the possible destinations, and Great Circle Mapper will map them all together.

This allows you to easily compare distances of all cities from a given origin, such as when we’re thinking about the Cathay Pacific and Cathay Dragon routes that Aeroplan members can now book online:

This syntax also works if you have a multi-segment path with fixed airports everywhere except the final destination, which can vary.

So let’s say you’d like to fly Toronto–Lisbon on TAP Air Portugal, but after that, you’re trying to figure out which other cities in Europe you can reach without overshooting the 4,000-mile threshold. You might input something as follows…

…and you learn that Madrid and Casablanca will work, but Barcelona and London wouldn’t.

However, the syntax doesn’t work if you’re trying to vary an airport in the middle of a routing. So if you wanted to compare two possible routings between fixed origin–destination pairs, you’d need to input them separately:

3. Comparing Flight Distances

The new Aeroplan employs relatively loose routing rules, and its complex but comprehensive one-way bound logic will treat any routing as “logical” – and therefore ensure validity within a single one-way bound – as long as it follows the general rule of thumb of being no more than 100% over the direct distance between the two cities.

That might sound very complicated, but thankfully, Great Circle Mapper makes it easy to calculate this. By inputting syntax of the form “AAA-BBB,AAA-CCC-DDD-BBB”, it will automatically display the percentage by which the latter routing exceeds the former.

To illustrate, let’s try to determine whether the following routing would be a valid single one-way bound: Vancouver–Istanbul–Johannesburg–Singapore–Perth.

Since we know the one-way bound logic works iteratively, the first step is Vancouver–Istanbul, which is obviously a valid one-way bound. Then, we add Johannesburg into the mix, so the question is whether Vancouver–Istanbul–Johannesburg is less than 100% over the direct distance of Vancouver–Johannesburg.


The answer is yes – it’s only 3.7% above the direct distance. So we proceed to the next step: how does Vancouver–Istanbul–Johannesburg–Singapore compare to the direct distance of Vancouver–Singapore?


Oof, that’s mighty close, but it does exceed 100% by just a hair. We’ve been told the 100% figure is only an illustrative general rule, so maybe there will be some leeway here, but I wouldn’t be surprised if the bound in fact breaks in Johannesburg and the remainder of the itinerary forms a second one-way bound instead.

4. Mapping Ranges

Upon first seeing the new Aeroplan’s distance-based award chart, many Canadians will naturally ask, “So, which cities are within which distance bands from where I live?”

Therefore, an additional Great Circle Mapper feature that’s certain to be very useful is the ability to map ranges of distance from a given central point, which allows you to visualize the answer to this question.

Let’s take the example of a Toronto resident who wants to figure out which cities lie within 2,750 miles of Toronto, so as to remain within the reasonably-priced first three distance bands of the “Within North America” chart. The Great Circle Mapper syntax would be “2750mi@YYZ”:

This provides a very useful visual representation of where our traveller could go while remaining within these distance bands.

It’s important to note that, unlike the features we’ve covered above, the range-mapping feature acts a “preset” for all searches going forward, allowing you to input additional flight paths or additional ranges on top of it.

So now that we’ve input our range of 2,750 miles from Toronto, anything we enter into the input bar will surface on top of the map. For example, we could map out a few potential North American routes to verify where they’d fall against our preset range…

Or, we could input “2750mi@YVR” to add a second range depiction out of Vancouver onto our existing range out of Toronto. The portion where the overlap represents the set of North American cities that can be reached for reasonably prices from both Vancouver and Toronto.

You’ll also notice that the Vancouver range just about encompasses Hawaii, providing us with the very satisfying sweet spot of redeeming a one-way flight to Hawaii for only 12,500 points.

We can also layer multiple ranges out of the same city to visualize all the distance bands on any one of Aeroplan’s 10 new award charts.

For example, the following map depicts the 4,000-, 6,000-, and 8,000-mile ranges out of Toronto, indicating the cut-off points for the North America–Atlantic award chart from a Torontonian’s perspective.

(To generate this map, we had input “4000mi@YYZ”, “6000mi@YYZ”, and “8000mi@YYZ”, followed by the additional city codes.)

Even though these range-mapping feature is incredibly useful, you still must still keep in mind that the new Aeroplan calculates award costs based on distance flown, so the mapped ranges may not always correspond to the distance bands if there are no direct flights between any two cities.

5. Map Aesthetics

While this section won’t really matter if you’re simply looking to use Great Circle Mapper to calculate flight distances, I figured I may as well share my preferred ways to make my maps look prettier using the software.

Great Circle Mapper offers a variety of different Map Styles, and a trio of the most common styles are displayed underneath the map: Plain, Light, and Blue Marble.

The default view is Plain, which I find… well, exceedingly plain, and also makes it difficult to read some of the airport codes. That’s why I always switch to Light instead.

Who can read this?
Much better.

If you scroll down to the Map Controls section, you’ll find a lot more options for customizing your map.

The default Map Projection is “Best: Rectangular or Polar”, meaning that Great Circle Mapper will automatically determine whether the rectangular plate-carrée projection or the circular polar projection is a better fit.

The former tends to win out in most instances, whereas the latter is mostly used when routings are concentrated around one of the poles (since otherwise, much of the map would be obscured on the other side of the earth).

You can also customize the Map Projection to be always rectangular or polar, depending on your preference, as well as a few other oddball projections that don’t make much sense at first glance, but might be useful for visualizing round-the-world travel.

Sometimes, you might want to give each of your routes different colours on a single map. While you can customize the colour of all flight paths under Map Controls, the easiest way to customize the colour of specific flight paths is by using the following syntax in the input bar (note the American English spelling): “color:blue,YVR-YUL,color:black,YYC-YYZ”.

Each “color:” term specifies the desired colour of the flight paths following it, until a different colour is specified. The default colour is red.

I won’t discuss the rest of the aesthetics options in detail, but between all the customizable text colour, text size, point symbols, path thicknesses, map styles, and map projections, it suffices to say that you can generate some pretty crazy-looking maps with the all-powerful Great Circle Mapper.


While it was previously under the domain of aviation geeks and extreme travellers who liked to plan complex round-the-world trips, Great Circle Mapper is now entering the mainstream Miles & Points consciousness thanks to the new Aeroplan’s distance-based award charts.

This article should equip you with a basic understanding of how to use Great Circle Mapper to calculate flight distances, compare routings, and plot out distance ranges from a given city. Happy trip planning, and may your flight distances forever squeak in under the thresholds!