That's really interesting -- I like the cars-in-parking lot idea. I think one of the most valuable math skills is correlation. Rather than keep it *just* percentage or fraction of the car lot that's full, you could compare the percentage of parking lots that are full in five different cities and search for possible reasons. Try Phoenix vs Manhattan, for example -- real estate and parking fees are drastically different!

Also, the time that the photo is taken can be (somewhat) determined by relative length of shadow. You could compare 5 or 10 parking lots in similar areas but in which the photo was taken at a different time. You could even make a great x-y scatter plot to look for trends.

In my school, with a US -based curriculum, we introduce X-Y scatter plots in grade 5, and reinforce them in grade 6. I'm not sure about the UK curriculum, but Edward Tufte believes (and I agree with him) that an X-Y correlation plot is far more informative than a bar graph. I'm always on the lookout for ways kids can collect data that shows a correlation, graph it, and seek explanations for any relationship they discover!

Warren (aka Zip)