In China, we ues "南边“ more than “南部”. And when you can use “南部”，you can use "南边“，too in most cases. ( Also, we Chinese do not care the fifferences between 南部 and 南边 much.)Therefore, 1. for this problem: (Is it correct that for example I have to say: 香港在广东省的南边. (Because Hong Kong is not part of Guangdong) And: 广州在广东省的南部 (Because Guangzhou is part of Guangdong) ) I think thses two sentences "香港在广东省的南边. " and "广州在广东省的南部"are right ,and your reasons are correct. 2. for this problem: (So the following sentences are wrong？ 香港在广东省的南部. 香港在广东省的南边.) My answer is that they are not right completly and just look these sentences. 香港在广东省的南部.(wrong) 香港在广东省的南边.(right) 广州在广东省的南部.(right) 广州在广东省的南边.(right) 3, for this problem: (Or can I just use 南边 and 南部 interchangeably?) I want to say you can do it in most cases because we do not care the differences of the two words tmuch.( To be strict, the two words cannot be interchanged.) 4, for thim problem (补充说明: Also, is there a difference between 南边 and 南面？) My answer is yes. Similarly, in most cases,they can be interchanged but there are exceptions,for example, 这面墙的南面有张画。 这面墙的南边有张画。 The two sentences have the differently. --------Hope I can help you. You can ask me when you have any problem if it is convenient for you.

南边 - to the South of xxx. 南部 - in the Southern area. So in this case, 香港在广东省的南部 would be - Hong Kong is in Southern Guang dong provence. Whereas 香港在广东省的南边 means - Hong Kong is south of Guang Dong provence

As implied in the English meaning, 南边 = The southern side of 南部 = the southern portion of.

In China, we ues "南边“ more than “南部”. And when you can use “南部”，you can use "南边“，too in most cases. ( Also, we Chinese do not care the fifferences between 南部 and 南边 much.)Therefore, 1. for this problem: (Is it correct that for example I have to say: 香港在广东省的南边. (Because Hong Kong is not part of Guangdong) And: 广州在广东省的南部 (Because Guangzhou is part of Guangdong) ) I think thses two sentences "香港在广东省的南边. " and "广州在广东省的南部"are right ,and your reasons are correct. 2. for this problem: (So the following sentences are wrong？ 香港在广东省的南部. 香港在广东省的南边.) My answer is that they are not right completly and just look these sentences. 香港在广东省的南部.(wrong) 香港在广东省的南边.(right) 广州在广东省的南部.(right) 广州在广东省的南边.(right) 3, for this problem: (Or can I just use 南边 and 南部 interchangeably?) I want to say you can do it in most cases because we do not care the differences of the two words tmuch.( To be strict, the two words cannot be interchanged.) 4, for thim problem (补充说明: Also, is there a difference between 南边 and 南面？) My answer is yes. Similarly, in most cases,they can be interchanged but there are exceptions,for example, 这面墙的南面有张画。 这面墙的南边有张画。 The two sentences have the differently. --------Hope I can help you. You can ask me when you have any problem if it is convenient for you.

“香港在广东省的南边”比较好一点，如果一定要说明“南边”和“南部”的区别，以香港在广东省的那边为例子。广东省是一个省，香港是一个特别行政区，香港在行政上不不属于广东省，所以，不能说“香港在广东省的'南部'”。用"南部"这个词来说明一个整体和部分的关系。而用“南边”这个词，没有任何整体和部分的关系内涵。举个更好的例子:广州在广东省的“南部”（广州属于广东省，广东省是一个整体，广州属于一个部分），中国在蒙古国的“南边”（中国和蒙古国是两个不同的整体，所以不能用南部，只能用南边）。相对于“南边”和“南面”，这两个词可以互换。例如：香港在广东省的南边（面）。中国在蒙古国的南边（面）。