Longitudinal Coherance is the final of the four key aspects that Ma (2010) describes to be linked to having a profound understanding of mathematics.
Children need to be given the opportunities to develop confidence and coherence within mathematics. Having longitudinal coherence is when you can identify recurring themes and to see the relevance.
Wu (2002) describes longitudinal coherence as being able to see the interrelationships among topics. Seeing these relationships will allow for coherent development.
I believe longitudinal coherence to be when you have a fundamental understanding over mathematics as a whole. This allows you to explore and experience situations.
Ma (2010) describes Longitudinal Coherence to be using what has been learned during our mathematics journey to influence and support our current mathematical status.