You can use a Particle System. Use your terrain as the emitter and the people as either an Object or a Group (Set their Origin to the bottom).
Set the Start and End time to 1.
Under Velocity change "Normal" to zero.
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/ubdJV.png)
Choose either Object or Group (You'll need to separate your planes in Edit Mode press "P" and select Loose Parts). "Object" would be choosing one plane/person as the particle. With "Group" you could choose any number of planes/people for more variety (Select the planes in Object Mode and press CTRL +"G" to Group them).
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/ZRmbU.png)
Additionally you can have control over the Particle Systems density by Weight Painting and a Vertex Group. With your Emitter selected go into Weight Paint Mode and select an Add Brush (There also is a Subtract Brush).
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/9sGoI.png)
Preform your Weight Painting. Blue represents the most density and red the least. Colors in between vary the density. This creates a Vertex Group with the default name "Group".
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/Z9IeV.png)
Go back to the Particle Emitter and under Vertex Groups > Density select or enter the name "Group".
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/2qRMG.png)
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/ReKEL.png)
![enter image description here](https://cdn.statically.io/img/i.sstatic.net/4k3XO.png)