Since the time humans appeared on the planet, we’ve been trying to make sense of it.

One way we do this is by  turning it into a picture… or rather, a map. Maps are incredible tools for navigation, but that's not all they are.

Maps shape how we view the world and can tell us how it was viewed and what we as human beings understood at the time the map was made. Today we’re talking about 5  maps that changed history, some that changed it for the  better, and some that are … maybe up for debate. [Intro Music] Let’s start with the oldest map on our list: Eratosthenes’ World Map, from as far back as 194 BCE. It’s not just the map itself  that makes it revolutionary, it’s also who made it.

Eratosthenes was one of those ancient Greeks, and he’s considered one of the  founding fathers of geography. His most famous accomplishment today is that he managed to calculate  the radius of the Earth to within 1% of the correct value – 6366 kilometers instead of the correct 6378. As for how he did this without a calculator?

Apparently it’s Basic geometry Ancient Greek scholars already  knew the Earth was round, so they also figured out that  if you calculate the distance between two cities, and measure the angle that  the sun hits in each city at the exact sample time, on the same day in each of those two cities, you can calculate the radius  and circumference of the earth. Which sounds easy, but in their defense, everything  was a lot harder back then. You can’t be in two places at once  so he had to go to one city one year, and the other city the next  year at the exact same time.

To get the distance between the two cities, he had to hire someone called a betamist which is basically someone who is trained to take perfectly equal length steps to survey an area of land. He was a little off because his  measurements weren’t exactly precise, but his math mostly checked out. These calculations were foundational for the coordinate system  he used in his famous map, a coordinate system we still use  today called Parallels and Meridians.

More commonly known as latitude and longitude. These lines are essentially reference  lines for where on the Earth we are, and using them on an actual  global map made navigation much more precise than it had  ever been before the map was made. Earlier maps were great for  showing relative locations, but they were more conceptual  and not much use for things like calculations and long distance navigation The introduction of a  mathematically based grid system like parallels and meridians  completely revolutionized map making and turned it into a precise navigational tool.

A tool that had a BIG impact on our ability to create this next map. The Cantino Planisphere dates back to 1502 and was named for Alberto Cantino, who smuggled the map into Italy. It's one of the first maps on record  to depict North America clearly and distinctly as its own continent.

Most earlier maps either didn’t  show the North American continent or labeled it incorrectly, as part of Eastern Asia. When the planisphere was made, any document containing details  about the so-called “New World” was closely guarded because countries in Europe wanted the information for themselves. The map was even stolen at one point, but it was found later hidden in a butcher shop.

This map and maps like it mark the start  of a transition between two worlds, the ones that existed before and after  European powers colonized North America and changed it forever. It also represents a transition  in the world of mapmaking itself because it's the first map to include the equator, the tropics, and the Arctic circle. Half the Cantino Planisphere  uses parallels and meridians, while the other half uses a technique  called the portolan-chart model.

This model is essentially the  earliest known type of nautical chart. It's created by mapping ports  along accurately drawn coastlines and drawing straight lines  between ports for navigation. These straight lines were the heading That you would follow to get to your destination, but this only worked within short distances.

Nautical charts didn’t account  for the curvature of the Earth, causing big problems the  farther you go out to sea. But it was still a huge leap forward The creators of the Cantino Planisphere essentially combined the detailed  and coastal navigation uses of the portolan chart model, with the long distance navigation  ability of parallels and meridians. Next up is the map you’ve  probably been waiting for.

If you’ve been going “are they gonna  talk about the Mercator projection?” then yes, it’s time to talk  about the Mercator projection. The mercator projection is infamous. A few months after I started in my PhD program, I went out for breakfast with everyone who was starting the  program at the same time as me.

And we had exactly the kind of conversation  you would expect from a bunch of geologists which was asking each other what  our favorite map projections were. My personal favorite as the  resident marine geologist, of course, is the Spilhaus projection from 1942, because I’m obsessed with the ocean and it’s basically the world as one big ocean. Virtually no one, when asked their favorite, would name the Mercator projection.

The Mercator projection was created in 1569 and it essentially projected  a globe-shaped object, the Earth, onto a cylinder, and that cylinder was rolled out in all directions to make the map. This was useful for several  reasons believe it or not, but had an unfortunate side effect. Since you are stretching the small surface areas around the poles out to cover the same distance on the  map as the bigger areas at the equator, it artificially inflates the size of  countries as they get closer to the poles.

If we look at a Mercator projection map, Greenland is shown about the same size  as the entire continent of Africa. In reality, Africa is actually about  fourteen times larger than Greenland is! This is also the most widely  used map projection out there, and this is why people hate it.

We were basically gaslit about  the size of different countries our entire childhood. Any map projection is going  to distort things somehow. But the fact is people often  equate size with importance, and it’s the western world that benefits most from this projection and that’s a problem.

If maps can cha+nge how we perceive the world, this one may not be changing it for the better. Still, it was made this way for a reason. The way this projection is made, every line intersects at a 90 degree angle.

This means that if you draw a straight  line from one area on the map, all the way across to another part of the map, the bearing that your ship has to follow stays the exact same for the entire  journey, across the whole globe. It sounds obvious, but that’s not the case for maps that  don’t use the Mercator projection. It makes navigation way, way easier.

And that's what it was made for, to navigate. It’s also the best one for using online, which is why it's stuck around so long. The perfect angles make it easier for  computer programs to zoom in on it.

So the Mercator projection  is great for lots of things, just maybe not the best choice for a classroom. This is what's known as the  Broad Street Cholera Map, created in 1854 during a  cholera outbreak in London. In the 1800s, most disease outbreaks were  blamed on breathing in bad air.

This was called the miasma theory. Hygiene and plumbing standards at  the time were basically nonexistent, and since disease often popped  up in the smelliest areas, people assumed that the smell  must be what carries disease. But a number of doctors had  suspicions that this wasn’t the case, including one named John Snow.

Long story short, he meticulously tracked the  source of a cholera outbreak to one specific water pump  on London's Broad Street. John Snow published his findings, including this map of the outbreak, and his story has become legend  in the world of geography. He went from door to door mapping  the locations of the deaths, found the source of the cholera, and singlehandedly stopped the outbreak, saving the city of London.

At least, that's how the story usually goes. But a lot of that story may be an exaggeration. Sorry, geographers.

Some versions of the story say he made a plea to the Board of Broad Street Parish to remove the pump, others say he went and destroyed the pump himself. But Snow never claimed to have removed it himself. And even if he did get the board to remove it, the outbreak had started slowing down on its own well before the pump's removal.

There’s also the matter of the map itself. He was the one to publish it, but there’s not actually any evidence  he used it to identify the breakout. He was thinking geographically, as far as keeping track of the location, so it’s still a really big win for geographers, but the map itself probably  wasn’t how he figured it out.

It’s also been claimed that  he was the first person to put disease outbreaks on a map, yet we have this map of a yellow  fever outbreak in New York City dated nearly 60 years before Dr. Snow made his map Despite the embellished  elements of Snow's story though, his work still had a huge impact. He showed how a deadly  disease was being transmitted, plus he showed that miasma theory  didn’t explain how cholera spread.

He also provided the alternative to miasma that eventually became  accepted as scientific fact, and popularized an entirely new way  to look at how disease was spread. The study of epidemiology today has  been profoundly shaped by his success. It just might be due to the  myths about his research as much as the actual research itself!

The final map on our list and my personal favorite are the NASA Landsat maps. Landsat is a combination of the words  “land” plus “satellite,” LANDSAT, and if you’ve ever clicked around in Google Earth, you’ve used a Landsat map. These are maps that show the  entirety of Earth's land surface from satellites orbiting more than 650km away.

They were the first of their kind, and they didn’t just change  our mapping capabilities, they changed the entire field  of Earth and Space science. They were launched in the  70s as part of a joint effort between NASA and the United  States Geological Survey, with the goal of creating the first visual  long term record of the surface of the Earth. They wanted to not only visualize, but also monitor for changes  in Earth's surface over time.

Each satellite crosses over  the same point on Earth at nearly the same time of  day, every 16 or 18 days. And once the satellites were in place, scientists had access to all kinds of  data that they had never had before. The satellites can see through  shallow water, helping ships navigate.

And the maps are used for  agriculture, monitoring crop health, and investigating water shortages. They’re used to combat wildfires  and plan the development of cities. And they’re used to study the  melting of glaciers and icebergs The satellites also have something  called multi-spectral imaging.

This means it can see wavelengths  of light that we can’t. This is important for my field of volcanology especially because when Landsat passes over a volcano, it can visualize the heat emanating from it! My job before my PhD was working as a lab tech for the Alaska Volcano Observatory, and images like this one of an  eruption from Shishaldin volcano were absolutely vital to the  work my colleagues put in to keep people safe from volcanic eruptions.

And if you’re saying “wait, Denali! I didn’t  know Alaska had a volcano?” Not only does Alaska have a volcano, we have over 130 of them. And we’ve had one or two of them erupt  just about every year since 1900.

How do we have room for  that many volcanoes though? Well as someone from Alaska, I’m obligated to remind you that  you could split Alaska in half and Texas would be still only  be the third largest state, with the 1st and 2nd largest  being the two halves of Alaska, so we have plenty of room for volcanoes. For once though the misconception that Alaska isn’t that big isn’t the  fault of the Mercator projection. it’s the fault of geographers  from the lower 48 exiling Alaska to a little corner next to Hawaii  on all of our national maps.

Landsat maps have even helped  us discover brand new places. There was an island in the Arctic  that’s inhabited entirely by polar bears that we only discovered  because of Landsat in 1976, and thus we promptly named it Landsat Island. Not only did scientists get access to  all the amazing data from these maps, so did everyone else!

Landsat was one of the first ever global  efforts to create open source maps that everyone could look at free of charge. Anywhere in the world you want to explore, you can do it right now from  your home using landsat imaging, and that’s how it really changed the world. [ outro ]