I am usually blogging about programming issues in my blog. Occasionally I like to write guest post in the "travel" category. I like to link the post from my blog as Other interest. Both are entirely different categories. Should I give the
rel="nofollow" to those links?
Even if categories are different, I think you shouldn't add the
rel="nofollow" attribute to your links. As you said, you like to link the post from your blog, thus it's a natural link and search engines like natural links.
If you would be able to link your website to a travel category it must be somewhat relevant. Adding a
nofollow tag could help you better from avoiding Google algorithm penalties as well.