In 2003, he was tasked with taking a set of photographs featuring China's railways to welcome the Beijing Olympic Games in 2008.

During that project, Zhan came up with the idea of simultaneously photographing ethnic groups.

With the privilege of free train travel as a railway employee, Zhan traveled more than 300,000 kilometers in a seven-year period for the project.

He recorded his entire journey in 1.2 million words in 22 photographic diaries.

"Before I started, I spent eight months looking up information, including the distribution, locations, cultural and local customs, and historical changes of ethnic groups," he said.

"Therefore, I focused my photography on ethnic dwellings that can represent their customs, migration and integration well.

"From the dwellings, we can find evidence of caves, tents, houses and other forms during the process of human development. They can even tell the historical changes of a nation, as well as the balance between man and nature."

During the project, he visited more than 500 ethnic villages in 50 regions.

"Even in the same ethnic group, residents in different regions have different characteristics in dwellings and lifestyles," he said.

"For example, in the pastures of the Tibet autonomous region, Tibetan residents usually choose to live in tents, while in the farming areas, residents choose dwellings made of earth, stones and wood."

The long journeys also brought him lots of unforgettable difficulties, such as the lack of food in the mountains, poor road conditions and walking dozens of kilometers on mountain roads to get to remote villages, especially when he had to carry 20 kilograms of photographic equipment.

"However, the hardest part for me was communicating well with local residents," he said. "I was often rejected by my interviewees for various reasons."

But he worked hard to win their trust.