Write about what you know!

Ben Macintyre, in The Times, was writing about a woman named Favell Lee Mortimer who published three volumes of travel writing covering Europe, Asia, Africa and the Americas yet she had never been to any of these places. Either she had made it all up or copied from other travel writings. He then mentions novelists "depicting places they have not seen."
I recall a meeting in Cardiff in which two well known crime writers spoke about their works. One said how he meticulously researched all details so that he would not be caught out by readers; the other who said he didn't do much research and didn't care if there were errors. Indeed, he had created an Indian detective who lived in Calcutta, a place the author had never visited, but no one had ever pointed out any problems with setting or plot; in fact, he said, he had once received a letter from a man who lived in Calcutta complimenting him on how wonderfully he had described the city and its inhabitants.
You are always advised, when you start out as a writer, to write about what you know. Codswallop. Write about what you want to write about, that which pleases you, not about your dull, ordinary life which will not be of much interest to others. In other words, use your imagination.
That's the advice of someone who has had one children's novel published - in Welsh!
Incidentally, Favell Lee Mortimer, in her imaginary travels, described the Welsh as "not very clean". Thank you Favell Lee Mortimer. She had probably seen pictures of miners coming up out the pits after a hard day's work, covered in coal dust.