Last year the FAA established new standards for the commercial operation of unmanned aerial vehicles (UAVs, drones, etc.) in US airspace. What that meant for me was that I could no longer use my drone for what I had originally purchased it for without obtaining a Small Unmanned Aircraft Systems Airman Certificate. I am in the process of doing that now and have spent the last week or so studying for my Aeronautical Knowledge Test.
I've spent about a week studying the material and like most exams (the ARE, the bar, etc.) some of the material covered is of dubious importance. For example, I've learned all about runway markers even though my quadcopter doesn't need a runway to takeoff. Still, I now know what the colored markers mean that are pictured on the left side of our rendering of our design improvements for the Stinson Municipal Airport Control Tower. The yellow "B" on the black background indicates that is Taxiway B and that the white "32-14" numbers on a red background indicate that taxiway is about to cross runway 14/32.
One thing that has been worthwhile to learn is how to read a VFR Aeronautical Charts (see above). Produced by the FAA and updated every six months, these so-called "Sectional Charts" are designed to give pilots the information they need to navigate under visual flight rules. As such they illustrate and label landmarks that would be visible from the air (cities, roads, lakes, etc.). But overlaid on top of that are several layers of information that is completely invisible.
For example you also see the multi-colored concentric circles you see describe the various classes controlled airspace that surround various airports. The solid magenta circles you see around San Antonio and Austin are for the "Class C" airspace that surround San Antonio International and Austin–Bergstrom International Airports. This type of airspace exists as "inverted layer cake": the inner circle represents a layer that goes from the ground all the way up to 4,800 feet whereas the outer circle represents a layer that starts at 2,000 feet and goes up to 4,800 feet.
Plenty of other information can be found here as well: control tower radio frequencies, the location and height of large obstructions and areas where the military conducts low-altitude operations. Almost everything a pilot needs to know can be found on the charts. Even current weather conditions can be found by listening to the Automatic Terminal Information Service (ATIS) broadcast whose radio frequency is provided on the Section Chart.
The density of information is part of what makes these charts so compelling. Seeing your world rendered in a way you don't normally see it is equally fascinating. It's like looking at an aerial photo of where you live in Google Earth: the landscape it renders is both familiar and foreign at the same time. It is also abstracted in a way that I would argue is beautiful.
For an even greater level of abstraction, check out IFR Aeronautical Charts (see below). These documents are for pilots using only their instruments and so provide no visual reference to what's happening on the ground. Instead all that is rendered are the invisible airways and waypoints that crisscross the sky above us.