Finding the Way in Wadi Hadhramaut

We look at georeferencing a map from Freya Stark’s travels in south Yemen, 1936, in this post.

So I’m a bit of reader in my (ahem) spare time and am firmly in the camp of Scout from To Kill a Mockingbird, who said, “…I never loved to read.  One does not love breathing.”  Of course she also said, “I still don’t see why I have to wear a darn old dress,” but that’s another story.  Most recently I’ve been reading a book by Freya Stark, who in the 1930s was a remarkable traveller and a bit of a trailblazer for her time.  She had no qualms about travelling to challenging places and spoke Arabic (among other languages), which helped immensely.

In Arabia, she travelled on her own, guided by Bedouins at times, but always up for a new adventure.  This book, The Southern Gates of Arabia, details her travels into the Wadi Hadhramaut of south Yemen.

Wadis are generally thought of as dry valleys where water only flows after heavy rains.  Yemen is very mountainous country, arid and dissected by wadis in all directions, many opening into the desert of Al Ruba’ Al Ghali, the Empty Quarter, that covers much of the Arabian Peninsula.  Here’s a satellite view of some of the wadis in the Hadhramaut:

(Fractals anyone?)

One of Freya’s main destinations was the Wadi Hadhramaut, fabled as a key source of frankincense and the mud brick skyscrapers of Shibam, the “Manhattan of the Desert“:

The origin and meaning of “Hadhramaut” is unclear, often translated as “death has come” (in the form of several different people), though may also relate to the original inhabitants or could also be tied to the Greek for water stations along caravan routes.  In any event, it’s an intriguing place.

This book really resonates with me as, in a previous life, I lived for a few years in what was then the Yemen Arab Republic, teaching English as a Peace Corps volunteer.  Here’s a National Geographic basemap to give you a sense of where I’m talking about.  We’re at the southern end of the Arabian Peninsula – that’s the Red Sea on the left and Djibouti and Eritrea to the southwest across the Bab al Mendeb (the “Gate of Tears”).  Oman is to the east and Saudi Arabia to the north.

Very formative times for me – click here (please!) for the view from my old house (now a hotel) in Sana’a’s old city, one of the oldest in the world:

(Sigh…)

At the time I was there, Yemen was divided in two along political lines, with the north being a republic and the south being one of the most Marxist states in the world at the time.

Being an American, I was not allowed to travel to South Yemen and the closest I got was seeing a distant, heavily fortified army checkpoint across a high plateau, making the south a mysterious, exotic place.  Once a British protectorate based around Aden, geopolitics battered that part of the world until, by the late 80s, it was quite far to one end of the capitalist/socialist axis.  The two united in 1990 but it hasn’t always been a successful venture.

I’ve really been enjoying this book – its prose is very evocative and makes me yearn for these arid desert regions, heavily bisected by dry wadis flowing off in all directions.  As you might suspect for a travel log, she mentions lots of place names which don’t appear to be used these days, which makes it a bit difficult to follow exactly where she is.  To be fair, there is a map in the book, but it’s frightfully difficult to make sense of, both because of its size and resolution (I find it very hard to read), and also because there are few features to help place it against a modern map.

I’m enough of a geography nerd that I read it with Google Maps open at my side and try my best to relate the text to the map, with little success, I might add.

So I thought, why don’t I use GIS to help me out here?  (Ed. What a nerd…)  I started with a quick internet search for map images.  Maybe someone else has already done this?  I did have a bit of success, finding this image, from a 1939 map:

Her route is shown as a dotted line on this map.  The problem here, of course, is that this was originally a piece of paper that has subsequently been scanned into an image.  Being an image file (a JPG to be exact) makes it a raster layer, which can be added to map.  While the content of the map is spatial (i.e. what the wetware interprets), the data (pixels) themselves are not – this map has no place in the world.  If I add it to a map, it won’t display at the correct location.  The image does have its own, built-in, coordinate system, with pixels as its units, and the origin (point of 0,0) at the lower left hand corner, but it is self-contained and doesn’t relate to the “real world”.

Happily, the process of georeferencing allows us to take this orphan and give it a home.  With this process we link features visible on the map with their correct location in geographic space.  We’ll be relating the image’s coordinates to geographic coordinates and I’ll then have a better sense of where her travels took her.

Because it’s a raster layer, I can add it to a map – but without a geographic coordinate system, Pro does its best and uses the built in coordinates to place the image’s origin at latitude 0 on the equator at longitude 0 on the Prime Meridian, too small to see within the red circle:

Once I click on the image name in the Contents pane, the Georeference button is available under the Imagery tab:

Clicking that opens the Georeference toolbar:

With these tools, and more specifically, the Add Control Points tool, I can create the links.  Clicking the Fit to Display button, , shifts the image roughly to the map space:

Now, using Add Control Points, I can set up links between what I see on the map image and where they should be on the surface of the earth.  I do this by first clicking at a point on the image and then where that point should be in the data space (here, the basemap).  The only places I’m feeling confident about identifying are Al Mukalla, and Balhof, both on the coast.  Al Mukalla (where Freya started her travels inland) looks like a good place to start, so I click once there, turn off the image and click on where it is on the basemap.  This image gets shifted so these points coincide:

I’ll set up control points between Balhof and it gets shifted and resized (with a bit of transparency so you can see how the two are related better):

You can see that the coastlines are hugging fairly well here.  Next I’ll do my best to pick up some key features that I can make out on both.   Here’s how it looks with a few more points:

Notice how the borders of the image are starting to change.  This is the result of different methods (algorithms) trying to best fit the points together, and treating the image like a sheet of rubber, stretching and compressing it to get a good fit.  There are no doubt some inherent distortions in the original drawing, made worse by time, that means it’s not a perfect fit.  In comparing the map image to what I can see on the basemap and satellite image, I think I’m getting reasonably close to reality, but given the distortions, I’ll never get it exact, I’m afraid.  More points doesn’t necessarily mean a better fit (though it’s tempting to think so) and I’m happy enough to stop there.

When I finished with my control points, I could just leave things as they are on the map.  The image itself has not been changed, just its appearance, but I can save a copy of the layer with the geographic transformation by exporting it to a new image.  Now it can stand alone and knows its place in the world

Now I’ve got a permanent image which has the location built-in.

Next, I’ll create a line feature layer and digitise in the dotted line on the map (this could be a new shapefile or a line feature class in a geodatabase):

And here’s the route with the map image turned off:

Now that I’ve got a data layer, I’ll also throw that onto a 3D scene, just for kicks:

Nice!  So now I’ve got a bit of a companion to the text to help me better understand her route.  I know it’s far from exact, given that it comes from a hand-drawn map, but it helps, methinks.  I could go a next step and add in some of the point data to better place events in the book.  Interesting to note that some of her route follows what are now established roads, though certainly not all.  This area was one of the main sources of frankincense back in the day so much of her route was along the caravan routes of the ancient Incense Roads, linking Yemen to Athens, Rome, Isfahan, Byzantium and the wider world.  (Hmmm…if I can find a map of the caravan routes, I could georeference that as well!)

Georeferencing is a powerful tool for taking paper or scanned maps and giving them a place in our GIS database.  Once you get the hang of it, it’s a great way to make the most of non-spatial spatial data such as old maps (if that makes any sense…).  In this post, we’ve looked at some recreational georeferencing, but I can think of a lot of examples where maps in journal articles, or historic maps, or even digital photos of maps have been blended into existing and more recent data layers.  Sometimes they’re used as basemaps to create features on top off (as I did above) while other times they’re just used to provide some spatial and/or historical context.

I’ve long wanted to work up a collection of maps showing where key books have taken place (e.g. On The Road), and georeferencing is one way to get that started, provided we can tie them to real places – this one might be a bit of a challenge:

“Middle Earth Map” by Kevan Emmott is licensed under CC BY-NC-SA 2.0

And why let things being off-planet put you off?

All these could be georeferenced provided you can link what you see on the image to known places (data) in your GIS data (and, yes, data for Mars do exist).

Sadly, I must end this post on a down beat.  The part of the world we’ve been focused on here is neither a happy nor a safe place these days.  And the saddest part is that it hasn’t been for a very long time.  The two Yemens united in 1990, then fell apart in a civil war not long after, before coming together again in a very tentative and volatile unification.  After a short period of relative calm, war again broke out in 2011, then later in 2014, with both internal and external provocateurs, accompanied by famine and, of course, Covid.  To the Greeks, Yemen was known as Arabia Felix, happy Arabia.  I’m so saddened that it’s been anything but in the past 20 years.  The Yemen I carry around in my head hasn’t really existed for quite a long time and I have no way of knowing how any my friends there are going.  Freya Stark wouldn’t recognise it either, and we might sigh together about the place we used to know.

Sigh…

C