A stunning new video shows how cities exploded onto the US map over the last 200 years

• A new video shows five major cities bursting onto the US map like fireworks over the last 200 years.
• The video comes from researchers at the University of Colorado Boulder, who used property records to clock where people settled and built from 1810 to 2015.
• Studying how cities developed over time could serve as a window into patterns of poverty and displacement.
• It could also teach us how to build smarter to avoid future natural disasters.

It took 200 years or less to develop major US cities like Washington, DC, Miami, and San Francisco.

But until recently, historians didn't have a clear picture of how those cities sprung up over time. A new study from the University of Colorado Boulder offers one of the most detailed looks at urban development in the US to date. The researchers used nearly 375 million property records to reveal where people settled and built from 1810 to 2015.

At the start of the 1800s, just 6% of the US population (around 5.3 million people) lived in urban areas. Today, more than four-fifths of the population (around 309 million people) do.

Most of the country's urban development happened in the last century, according to the study.

The video below shows five cities — Seattle, Phoenix, Denver, Miami, Washington, DC, and Rochester — bursting onto the US map like fireworks over the last 200 years. Blue pixels represent areas that are less developed, while red pixels represent the most developed areas. (Grey patches represent water.) Each pixel indicates an area of around 670,000 square feet.

Rochester developed first around the mid-1800s. Seattle, Washington, DC, and Denver landed on the map around the turn of the 20th century. Phoenix and Miami were built up later, around the mid-1900s, but by 2010, they were more widely developed than the other three cities.

While the common narrative is that urban expansion moved westward over time in the US, the researchers discovered exceptions to that rule. Denver developed much earlier than the rest of Colorado, and Miami developed late compared to the rest of the South, which the authors attribute to Florida's rough terrain. In many cases, the researchers found, individual counties started to develop even before their respective states were declared part of the US.

In the future, this research could be overlaid with demographic data to determine how Americans of various ages, races, and ethnicities inhabited certain areas over time — offering a window into patterns of poverty and displacement. It may also help illuminate which cities have been ravaged the most by natural disasters.

"Such new knowledge is highly relevant as it will tell us more about exposure of the built environment to coastal hazards, or wildfire — and hopefully teach us lessons what can be improved to avoid problematic developments in the past," Stefan Leyk, the study's lead author, told Business Insider.

How the US went from mostly rural to mostly urban

Prior to the University of Colorado Boulder study, historians had mostly used two methods to examine urban development: census records indicating where peopled lived, and satellite imagery showing how land was used over time. But there were limitations to those data sets. Satellite images only date back to the 1970s and often lack detail. Census data, meanwhile, is often missing prior to the mid-20th century.

The Colorado researchers found that property records from the real estate company Zillow provided a clearer portrait of urban development. These records allowed them to zoom in on individual areas — down to the size of a large office building or shopping center — over the course of two centuries.

Unsurprisingly, the researchers determined that where people built was strongly associated with where people lived. During the period of rapid development from 1910 to 2010, the US population density more than tripled. The image below shows how three Midwestern cities — Indianapolis, Indiana; Cincinnati, Ohio; and Dayton, Ohio — grew dramatically during that time period.

For the most part, urban counties have been expanding and getting denser since the 1840s. Between 1910 and 1920, the US went from being a mostly rural nation to mostly urban one. Expansion in urban counties dropped off between 2000 and 2010, while density shot up during that time period.

General trends, however, miss the differences between cities: In recent years, density has declined in Atlanta, steadily risen in Boston, and skyrocketed in San Francisco.

Still, US cities are nowhere near as dense as urban hubs like Jakarta, Indonesia (which dates back to 1527) or Seoul, South Korea (which dates back to 1394). That means there's still time to build more inclusively and prevent overcrowding. This new research might even serve as a roadmap.