If the type/length is a positive number of four or greater, then that feature is a region and is followed by that number of coordinate pairs. In a BNA file, regions are always "closed" (the last point in the region is the same as the first). Therefore, a triangle is expressed using four coordinates, with the first and last coordinates being the same point.
It's possible for a region to contain Island or Lake polygons. In a BNA file, islands and lakes have an identical representation. The basic representation is as follows:
"Object with Island or Lake", "NAME2",
"ID", n x1, y1
.
.
x1, y1 xx1, yy1
.
.
xx1, yy1 x1, y1The second xx1, yy1 pair closes the island or lake, and the final x1, y1 closes the main polygon. As you look at this structure, you can see that a "connecting line" is defined between the main polygon and the island or lake. Products that support BNA files can detect this line during import and remove it.
For more information on islands or lakes in a BNA file, contact ESRI.