Tissue tracing is  using heavy weight , but still transparent, tissue paper to make a tracing of a large plan.    We made tracings when it would take too long to use a protractor and scale ruler to make a drawing.   Once the tracing was completed, the edges were bound with masking tape on all sides to keep it from fraying or ripping.  The plans were rolled, not folded & handled with great care given all the effort it took to make the tracing in the first place.   We used pencils, not pens for the tracings & occasionally the work would be so intricate that a spray on fixative was used to keep the drawing from smudging. 

Much easier & faster nowadays to simply order a scale copy from the Registry or to print out plans  at home from the ROD website. 

In some ways I do miss the intricacies of the craft of title abstracting; but we all know that the only constant in life is change.