We have recently created a CCTV camera buying guide which should answer most of your questions relating to cameras and which one to use.
When people call us on the phone to discuss their needs they usually start by describing each area of the property to be secured. "I want a camera to cover my front garden which is 23 metres long by 18 metres wide. We need to cover the gate in the middle and driveway to the side and I'd also like to cover my ornamental fountain which is over by the neighbour's wall"
The problem with CCTV is that you can't cover vast areas with a single camera. Or rather you can, but the trade off is no one area will get special attention in terms of detail recorded. Even with high definition CCTV cameras once you widen the angle of what the camera sees recorded detail drops off dramatically. Think about it, you have a given number of pixels across the screen and as you move away from the camera the area the camera sees increases but that means the pixel density decreases. It doesn't help that many people selling CCTV tell lies and claim their wide angle CCTV cameras can film crystal clear detail at distances of 20 metres or more. Typically a 75 degree angle of view camera has an effective optical range of up to 3 metres in standard definition, 6 metres in HD1080P.
When that person looked around their garden they moved their head and focussed in on the areas of interest, the gate, the fountain and the driveway. A CCTV camera can't do this, it shares it's attention across the whole screen.
Zooming in electronically, increasing the TVL (number of TV lines) or increasing the number of megapixels wont help. You need to increase pixels by a factor of 4 to double the identification distance of the camera. The only way to get more detail in these areas is to optically zoom the camera in on an area, but it can only look in one place at a time. So there is a trade off with CCTV cameras, you either have a wide angle of view or you have good levels of detail. You can't have both.
Think carefully about where you actually need to film and how much detail you need to capture when calculating which CCTV cameras to use. Don't try to machine gun the whole of an area with CCTV, it won't work. Instead try to think of your site in terms of specific target points where you can capture information. Obviously there might be some instances where all you need is an overall view, but don't kid yourself that you will be recording footage from which you can read number plates or identify people. Here in our offices we have a camera which films the front car parking area. It can't be seen from the office and so we just want to know as and when someone arrives. A separate camera films them close up as they drive in to record number plate details and so on.
If you are planning a specific CCTV project we are always happy to help. We can look at your site using internet mapping from which we can take accurate measurements. At the same time we can chat on the phone to understand exactly what you want the CCTV system to do for you. From there we will be able to put together a list of equipment including the correct cameras. There is no charge for this and you are under no obligation.