To calculate the circumference of a circle, you can use the formula:
\[ C = \pi \times d \]
where \( C \) is the circumference and \( d \) is the diameter. Given that the diameter is 8 kilometers and using \( \pi \approx 3.14 \):
\[ C = 3.14 \times 8 \]
Calculating this:
\[ C = 25.12 \text{ kilometers} \]
Therefore, the estimated circumference of the circle is 25.12 kilometers.