I had to convert. 10 hectares.
For a square, that would be 316m on a side. Running around the outside would be 1.26km. An "X" plus 2 sides would be 1525m.
With a bit of bouncing around, that seems pretty reasonable.
500m x 200m: Perimeter: 1.4km. "X"+2sides = 1477 or 2077.
The feature density is probably the key, as kkling suggests.
The 2005 Ultrasprint at Kung Björns Hög near Uppsala used a 1:1,500 scale map of about 4 hectares: 200m x 200m approximately. The 2008 map is 1:1,000: Qual map 2008: http://www.dxdeluxe.se/2008/maps/qual.jpg
Interestingly, the qual map is 1.8km and the final is 700m: http://www.dxdeluxe.se/2008/maps/final.jpg
I'm not sure about the 2008 version, but the 2005 map I have has a crazy forking scheme that I've been itching to use.
Also, OCIN needs to plan a big Cincinnati-based A-Meet or sprint camp as an excuse to map the UC campus. If we can do it right, it would be amazing. I need to fact check this, but I think it would be possible to have a day of 2-3 sprints there with minimal overlap.