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