If the size of the ground area is $6 \, \text{km} \times 3 \, \text{km}$ and the corresponding photo size in the aerial photograph is $30 \, \text{cm} \times 15 \, \text{cm}$, then the scale of the photograph is $1$
If the size of the ground area is $6 \,\text{km} \times 3 \,\text{km}$ and the corresponding photo size in the aerial photograph is $30 \,\text{cm} \times 15 \,\text{cm}$, then the scale of the photograph is $1 : \underline{\hspace{3cm}}$ (in integer).