For example, if there is a L shaped sketch and you dimension from the bottom of the L to just above the horizontal part, and then you dimension the vertical part from the end point of the last dimension you'd be okay. But, if you dimensioned both of those lengths and then the total length you would be over dimensioning the sketch.
An interval may be described as horizontal, linear, or melodic in the music world, if that's what you were referring to.
