Temperature is an interesting value. It’s something all of us experience at every moment of every day. We feel the temperature of so many things that it becomes second nature; the air around us, our clothes, the things we pick up with our hands, the food we eat, the water we drink and bathe in. Since it is something we experience constantly every day, there is a myriad of ways to represent temperature to communicate it to someone else.
The primary method we use to communicate temperature is just a single number. This number could be on one of several different scales. The US commonly uses Fahrenheit, while the rest of the world has intelligently converted to Celsius, and some scientists use Kelvin. No matter which scale gets used, the number represents the amount of thermal energy there is per particle.
Dials are roughly the same as the number, but add some context. Typically the dial will be calibrated so that the high and low points are the likely minimum and maximum for the situation. This helps add some context to the value displayed. They are often used for outdoor thermometers because they can easily be read from quite a distance through a window. In addition, they can have very large displays, and are often controlled by a coiled spring on the back. As the temperature changes, the spring expands and contracts, causing the indicator hand to rotate. (Source.)
The most common length-based displays of temperature are mercury or alcohol thermometers. These use the changing density of a liquid to show different temperatures. This is similar to the dial displays, but it is slightly better at visualizing because it is not radial.
Color scales can work well for displaying temperature, as well. The warm and cool colors that many cultures recognize, for example, are often used for temperature color scales (these actually correspond to the light emission of black body radiators). Color displays of temperature are frequently used for maps or combined with other display techniques as in the outdoor dial thermometer above.
Many elements and compounds change color as they change temperature, and some even begin to emit light at high temperatures. In a sense, these colors are visualizations of temperature. (Source.)
Like any other quantity, temperature can be displayed in many different chart types. All the typical charts work wonderfully, however there is a special chart that works for temperature. The Psychrometric Chart is designed to show how air feels. It simultaneously shows dry and wet bulb temperature, humidity, enthalpy at 100% humidity, and the specific volume of the air. A single point on a Psychrometric chart shows all of these values (five dimensions). (Source.) With so many ways to represent temperature, just make sure you communicate it clearly. Poorly communicated temperatures can result in discomfort at best, and injury or death at worst. Drew Skau is Visualization Architect at Visual.ly and a PhD Computer Science Visualization student at UNCC with an undergraduate degree in Architecture. You can follow him on twitter @SeeingStructure