Camera Movement
Keyboard controls
We'll be using common key-binds WASD to control the camera and pan it across the play area. To zoom, page up and page down can be used as to not conflict with possible future key-binds.
The input axis "horizontal" and "vertical" take into account both WASD keys and arrow keys to add force to the camera's container object which also has a rigid-body element. There isn't a equivalent axis for page up and down in Unity's inputs, requiring the creation of one manually. However, for efficiency I have simply coded the inputs. The downside of this, however is that the player can't adjust the key-bind. This shouldn't be a problem at the moment, though as a control menu hasn't been implemented.
The code is simple; if page down is pressed then the camera's container gets a downwards force added which means the whole rig is consistent and doesn't leave us with any bugs that we might have whilst not using a rigidbody element.
Mouse controls
The mouse controls will consist of two things:
Scrolling via the mouse wheel and panning by moving the mouse to the edge of the screen.
This requires a proximity check which can be achieved by comparing the mouse position with screen positions.
Here, the mouse minimum boundaries are simply 30 units, which I deemed a good number for responsiveness and it is not too big as to disrupt the flow of gameplay in the center of the screen. The maximum boundaries are the screen width and height subtracted by 30. If the mouse cursor crosses these coordinates, then the camera is panned in the corresponding direction.
Next, we need to zoom using the mouse wheel. Unlike page up and down, the scroll wheel has a dedicated input axis already implemented within Unity, so we'll be using that.
I added the code to an original addforce function, however I needed to invert the scroll wheel axis and multiply it by 35 in order to get a big enough movement that feels natural.
Currently there is no need to add a rotation control to the camera, however if obstructing buildings and objects are added then this will be implemented. A lot of RTS games such as Starcraft and League of Legends don't include a rotating camera because often it isn't needed and sometimes even disorientates the player due to the change of perspective.