this is so/it is so.什么意思

this is so/it is so.什么意思原文如下：Last November I went to Hong Kong and visited Chungking Mansions repeatedly as I made a final research journey while writing the book. Filmmaker Terrill Lee Lankford went with me so he could document my research of the places that would be in the novel. This was so I could refer to video while writing about Hong Kong once I returned home. It was also so he could make small films that could be used to document and promote the book when it was published