A front as the boundary between unlike air masses, and a front is the edge of a transition zone between unlike air masses, because as we have seen a true distinct boundary can be difficult to discern. Fronts are found based on the distribution of weather variables such as temperature, pressure and wind. It is truly a matter of finding the best place for the front based on these variables, because nature rarely gives a perfect textbook case where all of the variables are obviously different.
There are 5 basic kinds of fronts:
Cold front--The leading edge of a transition zone where a cold air mass is replacing a warmer air mass
Warm front--The leading edge of a transition zone where a warm air mass is replacing a colder air mass
Stationary front--A zone where a warm air mass and cold air mass meet, but the masses are not currently moving
Occluded front--2 types:
Cold occlusion-‘Very cold’ air moving into ‘cold’ air
Dry line--(Special case)
A boundary between air masses with similar temperature characteristics, but different humidity characteristics
Finding fronts on a Map-Look for some of the following things on a surface map in order to identify fronts (In order of my preference!)
In general, warm fronts are more difficult to discern than cold fronts. Their transition zones are typically much larger and their affects much more widespread.
There are other introductory books that cover these topics, such as Meteorology: Understanding the Atmosphere by Ackerman and Knox, published by Brooks/Cole.
Additional information from WW2010, including identification on weather maps.