For he has left his footprints on around 3,000 hutong as part of a 16-year labour of love.

The determined old man has now set his heart on turning his painstaking research into a unique set of maps which will offer a fascinating insight into a rapidly changing city.

When Shu started his quest, he was confident he would be able to visit every lane in the old neighbourhoods he had targeted. It was just a question of time.

Thanks to his endless patience and willpower, a dream became reality.

"I set out to probe Beijing's old neighbourhoods on March 1, 1987. Up to now, it has taken me 16 years to walk through all the 3,000-odd alleys step by step. All these lanes have become the objects of my careful study," explained Shu, a retired engineer with Beijing Railway Management Bureau.

Based on what he has learned, Shu is now painting unique maps which aim to offer a panoramic view of all the lanes and important courtyard houses within the old city of Beijing.

Each map includes important residences belonging to influential historical figures, ancient government agencies, old-style bank houses, former educational institutes and religious buildings.

Shu also jots down anecdotes related to the interesting historical venues in the margin of his maps.

That allows people to discover the historical evolution of important locations in the old city while consulting his maps.

"Although some of alleys and courtyard houses have vanished in recent years because of the establishment of high-rise buildings and the broadening of roads, I still drew them on my maps in an attempt to save the past glory from oblivion," Shu explained.

Asked why he made up his mind to take on such an arduous task, Shu recalled a chance look at a map of Beijing drawn during the reign of Emperor Qianlong (1711-1799) in the Qing Dynasty (1644-1911) at a public library 16 years ago.

The map, 14 metres long and 13 metres wide, struck him as a masterpiece. It provided nothing less than a bird's eye-view of the whole city more than 200 years ago. Every quadrangle and its surrounding houses were drawn on the map according to the correct proportion.

The only shortcoming of the ancient map, he believed, was the lack of necessary Chinese characters indicating the names of different locations and the development of the city.

A sudden inspiration crossed his mind at that moment: "It seemed not a bad idea to draw a map showing the capital's changes over more than 700 years, namely, from the moment when Beijing was established in the early Yuan Dynasty (1271-1368) till now," he thought to himself.

After returning home from the library, he set about the investigation at once, preparing a bag filled with a camera, films, pens and note books.

As well as taking photographs of the valuable houses, Shu also set about estimating the length of every alleyway using different methods.

In the beginning, he used tape measures. But it was almost impossible for him to fix the tape measures at two ends of an alley.

In the end, Shu decided to use his feet to make the measurements. As he walked between two ends of a lane, he carefully counted the number of steps and then converted them into metres.

"Such a simple but efficient way made my work run smoothly," he claimed. "And it helped my map conform to proportion."

While more and more traditional residential areas have been renovated in recent years, a number of alleyways and courtyard houses with historical interest have been demolished, disappearing forever.

To keep up with the rapid pace of change, Shu would rush to reach construction sites ahead of the wrecking ball and bulldozers.

After learning that Yongkang Hutong, a lane near Dongzhimen, would be rebuilt, Shu got up at 4 am and took the first bus to the area.

In his enthusiasm to take a last look at the original layout of the alley, Shu walked up and down for several hours, taking as many photographs as possible.

Overcome by the feeling of regret after going back home, Shu painted the whole lane and its surrounding area overnight.

"I hope my map can preserve a little of the historical flavour that will disappear in the future," said Shu.

The enthusiast started to appreciate more than ever the value of time. A typical day would see him getting up at the crack of dawn to pay visits to old houses set for demolition.

Despite the satisfaction he has gained from his work, Shu has also faced his trials and tribulations down the years.

On one occasion, he was preoccupied with measuring the length of Lumicang Hutong in Dongcheng District. His investigations aroused the suspicions of a middle-aged woman who followed him for half an hour.

Eventually the woman, unable to contain her curiosity, challenged him and rudely asked what he was doing.

"I could tell from her look that she mistook me for a mad person," Shu recalled.

On another occasion, Shu met with unexpected humiliation. Attracted by a grandiose courtyard one day, he entered it with a view to dropping in on local residents.

In his enthusiasm, he failed to spot a "no trespassing" sign. Refusing to listen to Shu's explanation, startled residents sent for the police. Shu found himself sharing a cell with two common suspects for two hours until the matter was finally resolved.

Despite the hardships he has faced, Shu is determined to press on with his self-appointed task.

He added: "I am devoting all my time to drawing the maps of Beijing's old city. I consider them to be my babies and expect them to be born in the near future."