It is important to highlight that some CPM software can extract the data to draw the line diagrams from the schedule model but not all can correctly model the required volume of work distance. If your software cannot do it as Spider can then you might be better if planning your linear project not using such software.

http://www.youtube.com/watch?v=ciYVSAhOsJk

Spider Project Linear Diagrams presents project schedule as the chart that shows when and where (in project metrics) activities of different types will be performed.

The relationship is modeled trough production type activities and resource productivity, the lags are modeled using volume of work lag within the CPM model.

You can manage linear work as well as non linear work within the same model. Perfect for jobs like highways where road work is linear while work at the toll stations and bridges are not.

If the CPM software cannot model continuous feed through volume of work lag and only uses time lag the model will be wrong. In the following figure the distance between activities 1 and 2 is modeled using time lag while for activities 3 and 4 the lag is modeled using volume of work lag. As you can see even when volume of work on activity 1 the time lag tells activity 2 can start soon as no consideration to volume of work is modeled while between activity 3 and 4 you see a delayed activity 4 as it will not be able to start after the remaining volume of work necessary to keep the distance is realized. This volume of work lag is a relationship that must be continuously keep active untill al predecessor volume of work is realized, this can be modeled with volume lag but not with time lag as after initial time lag is consumed the link is no longer active.