Static allocation:
coord xy[500][460];
Dynamic allocation:
coord** xy = (coord**)malloc(sizeof(coord*)*500);
for (int i=0; i<500; i++)
xy[i] = (coord*)malloc(sizeof(coord)*460);
// and at a later point in the execution of your program
for (int i=0; i<500; i++)
free(xy[i]);
free(xy);