Structural graph theory, including graph decompositions, tree-structures, surface embeddings and minor-and topological-inclusions of graphs.
Maharry, John; Robertson, Neil; Slilaty, Daniel; Sivaraman, Vaidy; Flexibility of projective planar embeddings, J. Combin. Theory, Ser. B 122 (2017) 241-–300.
Maharry, John; Robertson, Neil; The structure of graphs not topologically containing the Wagner graph, J. Combin. Theory Ser. B. 121 (2016), 398–420. Special Edition by invitation - "Fifty years of The Journal of Combinatorial Theory"