ー is just a dash.
"The nobasu character (ー) ordinarily lengthens the vowel sound directly proceeding it"
But did not know that it "had" to be directly followed by katakana. :)
The ー character is typically used with hiragana and katakana to elongate the previous character's tailing sound: リー for the name Lee (rii), メートル for meter (meetoru), as examples.
The ー character is not used after kanji because their sound cannot be elongated.