Saguaro Land: Mapping the Sonoran Desert is harder than you think

Saguaro Land is a series from The Show looking at the Sonoran Desert — the lushest, hottest desert in the world that happens to be our home.

The stories will examine the desert season by season, through music, art, literature, food, drink, flora and fauna — and maps, starting with a look at where exactly the Sonoran Desert is.

Amy Silverman/KJZZ

But as it turns out, that’s not as straightforward a question as you might think. Mapping the desert is a challenging job and one that doesn’t have many clear-cut answers.

To try to get a sense of where the Sonoran Desert is — and where it isn’t — The Show reached out to Matthew Toro, director of maps, imagery and geospacial services at Arizona State University Library.  

Full conversation

MATTHEW TORO: We found, as we suspected, that any form of geographical classification is never black and white. There's always a bit of gray area and, and classifying ecological regions based on biotic or plant based communities or physiographic elements, you know, landscape features such as mountain ranges, etc., it complicates things. There's no sort of clean and simple answer, frankly.

MARK BRODIE: So did you find that different maps listed different sort of boundaries, I guess, for lack of a better word, for the Sonoran Desert?

TORO: Absolutely. And that's an artifact of the nature of map making and the underlying scientific data that goes into producing maps. And then ultimately, in addition to the data that's used to make those maps, the discretion of the cartographer, the actual mapmaker, in making essentially graphic design decisions.

But yeah, we did find discrepancies. And a lot of that has to do with the provenance of the data, where the data came from, the, as I said, the source of the data, but also the timeliness of the data. As scientific data collection continues in different teams of, from different types of scientific disciplines sort of compile and synthesize their data, the state of geographical, geological, ecological classification changes.

BRODIE: So this is obviously not like a political boundary map, right. This is more of an ecological, scientific kind of thing. So were those the criteria that you found the cartographers were using generally?

TORO: Absolutely. You know, it's far easier to map purely human constructs. Administrative lines, county divisions, census tracts, etc. But mapping nature is a far harder process. Nature rarely, if ever, gives any clear sort of clean geometric lines. Nature is inherently fuzzy. The distribution of plant communities isn't clear cut always. The geomorphology that led to the creation of certain mountain ranges. Yeah, it seems fixed by our timescale, but things change. So, yeah.

BRODIE: So how do you think then, given some of those discrepancies and given how different people interpret different criteria and different factors here, how should we determine where the Sonoran Desert actually is?

Like, how should we be determining, yes, this is part of the Sonoran Desert, or no, it's not?

TORO: Fortunately, there are very solid scientific precedents that take into account multiple sources of information from multiple disciplines. First and foremost, you have sheer physiography, the layout of the landscape, the elevation of things. You also have, as I said earlier, plant communities, vegetative distributions. Many people associate the saguaro, for instance, with the Sonoran.

But it's not perfectly contiguous, it's not perfectly overlapping. You know, there are areas where there might be some saguaros that aren't firmly classified as a Sonoran Desert. For instance, a Joshua tree is often associated with the Mojave Desert, but there are some sections of the Mojave Desert that have no Joshua trees whatsoever.

But if you combine multiple types of data, mostly physiography, ecology, distribution of different flora and fauna, you can come to some baseline consistent consensus among different scientific groups.

BRODIE: Well, you mentioned the Joshua tree and we saw one of the maps that you had found. There are parts of the Sonoran Desert that don't have saguaros, right. So that kind of adds another layer of complexity here.

TORO: That's right. And it's an unenviable task of ecologists and biologists and biogeographers, etc., to do this work. That's why the work of mapping still goes on.

You know, we think, oh, everything is mapped. We already have all this data. But no, we're always increasing our, the sophistication of our mapping methods, the sophistication of our data collection methods.

We need ultimately, boots on the ground to ground truth. A lot of these other sources of imagery or other sources of data, such as satellite imagery. And of course, all this data is accumulated and we stand on the shoulders of our predecessors to continue developing a more robust scientific record.

BRODIE: What is the relationship between some of the scientists, maybe even scientists in the field, who are studying the plants and studying the soil and studying the climate and the environment of different parts of the West, be it Sonoran Desert or not, and then the cartographers who are actually physically drawing the maps?

TORO: That's an essential relationship. There needs to be trust amongst the scientific organizations, among the scientists themselves, and that's why the scientific process of reproducibility and replicability is so important. There needs to be transparent pipelines, data pipelines, because ultimately we're really translating data collected with GPS receivers, ground observations, photographs, et cetera. And then ultimately it's one or a small group of cartographers who are putting it all together and publishing these seemingly authoritative map documents.

And we all take these documents as sort of authoritative and we take them for granted as fact. But is, you know, what happens behind the scenes to collect all that data is, is often messier and not as clear cut as we might like to believe. Humans love to simplify reality and compartmentalize the world. That's why we have maps that classify with different bright colored maps or different patterns, these different units. But nature is far more complicated, and that's why this work is so important.

BRODIE: Let me ask you kind of a philosophical question, and I'm wondering if you think that it matters if we know where exactly the Sonoran Desert is?

Like, for example, here in Phoenix. We know that we are clearly in the Sonoran Desert. I don't think anybody would argue with that. But does it matter if we have a map that says, OK, here is where the Sonoran Desert is and here is where it is not?

TORO: That's a great question. I love philosophical questions. I would say the most important, yes. To answer succinctly, yes. Classifying these geographical and geobiographical, these biotic ecoregions is essential. Primarily because of our human responsibility to conserve and protect these regions. Human policy intervention can only develop if we have baseline scientific facts to, to inform that policy.

So, you know, there might be some communities that reside, human settlements, human communities that reside at the border of two eco regions, if you will. Now, the significance of, you know, whether, whether that community, that human settlement is in one part of the Sonoran Desert versus the other is probably not that important.

Nobody really cares. But if we care about protecting the plants and animals and protecting the ecological diversity of the Sonoran Desert, then yes, absolutely, to inform policy, we need this scientific work to be done.

BRODIE: It sounds like what you're saying is it's more maybe important for us to appreciate where we are. If we know we're in the Sonoran Desert, we can appreciate it.

We can do what we can to maybe leave it better than what we found it, as opposed to, you know, not knowing where we are and just assuming, oh, we're you know, we're in Phoenix. You know, this is just Phoenix. It doesn't matter.

TORO: Absolutely. Geographical consciousness, claiming your city, claiming your community, claiming your ecology and being an active contributor to efforts to protect that ecology. It's really not, you know, we often think of ourselves as separate from our ecosystem, but we are a very dominant and very forceful and sometimes violent ecological actor. We need to be more aware of our geography and our ecology and the region in which we reside so we could be better stewards of those regions.