Last year was hotter than any other since record keeping began, but the entire globe didn't uniformly heat up all at the same time. Instead, different parts warmed up at different rates.
New NASA imagery (above) shows how that process happened. In 1880, for example, parts of the world were hot, but overall the temperatures were lower. By 2014, the situation was reversed: some places were still cool, but the planet as a whole was much warmer.