Why Beijing is Known as a "City of an Eightarmed Nezha"?

As learned from quite some people that the city of Beijing was shaped like an "Eight-armed Nezha", why is it so? Fictitious novel has it that Nezha, the Red Boy, is very forceful and brave. Only he is able to subdue the evil dragon in "Youzhou, the Sea of Bitterness".

The story goes like this; one day the emperor wants to build a city round Beijing. Nobody from the Board of Works dares to take up the job and has to invite imperial advisers out to make the decision. And so Liu Bowen, the chief adviser and Yao Guangxiao, the deputy are given the imperial order to carry out the work, but the two of them have different schemes in minds. So stands the case they agree to work out the respective blueprint of their own and pit them against each other ten days afterwards. Returning home they begin to rack their brains. However, they seem to have heard somebody whispering by the ear, "work it out after me and it'll do." Seeing nobody's nearby they seem to have lost in quandary. On the 3 rd day when Liu Bowen is out prospectingn he finds s boy in red shirt and pants following him while keeping a distance in between. And Yao Guangxing comes across the same boy when out on the survey that day. Pondering over the matter for some time they think the boy must be Nezha. However, on a second thought, it's not the Red Boy for he should have eight arms. One day afterwards, when Liu ia out with a butler he sees again the boy he saw the other day. Recognizing the very boy Nezha, he follows close by him, hearing again "work it out after me and it'll do". Gazing ahead, he can't find the boy anymore. Yao Guangxiao meers with the same case when he is out prospecting on the very day.

At noon the 10th day, Liu and Yao begin to make a comparison of the blueprints as agreed upon. After a while of back-to-back drawing, the blueprints turn out exactly the same pattern, a "City of an Eightarmed Nezha", The due-south Zhengyang Gate in the middle is the very head of the Red Boy, the two doors on the east and west of the jarred cit his two ears while the two wells inside the gate are the two eyes of him. As to the four gates of Chongwenmen, Dongbianmen, Chaoyangmen and Dongzhimen they are the left four arms of the Boy while Xuanwumen, Xibianmen, Fuchengmen and Xizhimen are the four arms on the right. The Forbidden City is the intenal organs of the Boy with the Tiananmen Gate as the inlet. The flat pavement in the middle of the Forbidden City is the esophagus for Nwzha while the two passages running north and south on the right and left are the two large ribs and lanes the small ones. When thus decided, Liu Bowen begins to lay out the city according to the design. This is how the name "City of an Eight-armed Nezha" for Beijing came to be known in the public.