Another thing to note is that the Qin were the first to conquer the far south. The present city of Guangzhou was founded by the First Emperor (though of course it was more a military colony then and was under a different name). The far south was not really made Chinese until many centuries later, but Qin developed a government presence there (instead of just small independent groups of Han settlers).
From Rafe de Crespigny:
"The lands beyond the Nan Ling divide were originally brought under Chinese control by the First Emperor of Qin. In a series of campaigns between 220 and final victory in 214, the armies of Qin conquered and annexed territories covering the greater part of present-day Guangdong, Guangxi and northern Vietnam, and there was at least a brief occupation of part of Fujian.52 With the fall of Qin a few years later, however, Zhao Tuo, who had been named as successor to the Commandant of Nanhai under the empire, took advantage of the disturbed conditions to the north to seize and block the passes through the Nan Ling, and he established his own regime. This kingdom of Nan-Yue continued under Zhao Tuo and his successors for almost a hundred years until it was conquered by the armies of Emperor Wu in 111."
During his reign, the first emperor also built a huge network of roads and canals to facilitate communications in the empire and some of these are still in use today. For example:
"This notable development reflects the importance of the imperial communications routes and the prosperity brought by trade with the southern coast. Under the empire of Qin, the highway which came south to Changsha had continued up the valley of the Xiang along the present-day railway line southeast into Lingling. Just south of the county of Lingling, by the present town of Xing'an in Guangxi, the First Emperor had a canal cut across the watershed to link the Xiang River with the head-waters of the Li. This remarkable feat of engineering, the Ling Qu "Magic Trench," initially constructed to aid the movement of the First Emperor's armies in their conquest of the far south, was maintained throughout the Han dynasty. It has been restored on occasion over the last two thousand years, and it is still used for traffic between north and south."
I think he also constructed roads directly connecting the northern borders.
The First Emperor's main priority was to unify the nation. So he standardised writing, weights, the width of carriage (so that they could all fit onto the roads), currency etc. Of course he standardised them on the pain of *death*. Communications was a vital part of this. He abolished feudalism and established the regime of provinces and the use of constantly rotating inspectors and administrators to rule them instead of kings. His ruling philosophy was to feed the trunk and starve the branches. Of course all the achievements of Qin were under the First Emperor. The Second Emperor was a total incompetent.
As XIII stated, the Qin helped define China for the next 2200 years
