Each black line connects consecutive numbers x and x + 1. Kropk'i Sudoku (see link below) had a similar feature.
These puzzles are fun and challenging. I've solved all the 4x4's, half the 5x5's and some 6x6's. I tried the 9x9's: no progress - yet.
The graphics for Joint Number Place are overdone. There should be no white or tan squares. The background should be black. The connecting lines should not have two colors. These are minor complaints.
Other Latin Square Puzzles
Futoshiki also known as Hi-Lo Sudoku