Maths: Election Rally Attendance Numbers

Phew! The NDA agreement I signed with myself has expired today, so I can start writing again. I've got a few entries backlogged. This one is about the election. I attended only one rally; the Last Night of the Proms at Serangoon. I wrote then in the forums...

I just came back from the Serangoon Stadium rally...darn it, this is the first time I've truly felt Singaporean... at the end LTK and SL led the probably the standing room only 40k crowd to recite the pledge in both English and Chinese... really class act campaign...

It was standing room only at Serangoon Stadium that night and many were turned away, but it didn't compare to the rally at Hougang held a few days earlier; the field there was much larger than the stadium. This picture by Yawning Bread was probably the iconic picture of the resistance movement in this election.

I was curious about one thing: how many people attended this rally? YB did some calculations based on estimates of the density of people within a certain area, then projecting the numbers to cover the whole field. He felt there were 100-120,000 people that night. Tym also attended the rally and she estimated that 10-20,000 people attended. Malaysian newspaper The Star mentioned 10,000 folks (via SGWatch).

There's quite a difference in estimates here. Was there another way to solve this crowded problem? I realised I did have another lead: Google Earth. I already know the capacity of the National Stadium. The rest is straightforward.

Step 1: Use Google Earth and find the two locations. Print both locations out using the same scale.
Step 2: Cut out the seats of the National Stadium.
Step 3: Continue cutting the stands and placing in on Hougang field.
The capacity of the National Stadium is 55,000 (source). You can see above that all the seats of the Stadium covers about half of Hougang field. I believe this is a conservative estimate. People stood at the rally, and they most likely stood very close to one another, compared to the seating arrangement found at the Stadium. Therefore, I think the number that night at Hougang Field was very nearly 100,000 people. YB's estimate was quite accurate according to this methodology!

Anyway, the folks who organised this rally won the Hougang seat, but lost the larger Aljunied Large Area Constituency in a close fight. More good years! (And thanks for the memories!)