So if I give valve credit in the map information, then its not stealing. its the same exact thing as writing a paper. when you use someone elses work in a paper, you give them credit in the works cited page or with annotations. it is not considered stealing if you give the original author or creator credit for what you have used. So there you go. I give Valve credit, its not stealing. You cant argue with that, and if you do, then every research paper you every wrote was also stealing.
thats not true, if you had to write a report on moby dick, and you just copy and pasted the whole novel, changed a few words, added an "in conclusion" to the end, and credited "Herman Melville" for the original, is that stealing? You bought the book, you gave him credit...
the answer is YES it IS PLAGIARISM. In your writing a paper example, you are only quoting very small snippets from the original work. Thats akin to opening badwater and copying over the payload cart, and crediting badwater for the payload entities. That is NOT the same as copying 100% of a map, changing a few textures, adding a sniper tower and crediting the person.
Something that drastic would require you to contact the author and get written consent to not call it stealing. Watch the movie Finding Forester, that issue arises.