In Flight Simulator, scenery designs are created using the BGL graphics language, but there are two different ways that you can create the final binary graphics program. You can create the final graphics program using graphics assembly language programs or graphics design tools.
The simplest way to create a graphics database is to write a few graphics commands and use an assembler to build the binary database. This is the method that was used to create the first Flight Simulator graphics databases, and it's still widely used today.
Graphics assembly language programs provide the advantage of enabling you to really see what is going into the database ; they also give you the ability to specify coordinates very precisely. The drawback is that you don't get any graphics feedback until you run the graphics program; that is, until Flight Simulator interprets the program.
Design tools are the alternative. Many design tools have been created to help designers design graphics databases. Some of the tools are interactive; you can move a cursor on the screen and click points into 3-D space. Others tools enable you to create a drawing on a data tablet and use a cursor to trace your design. Many of the design tools simply interpret your mouse or cursor input and create the graphics assembly language on the fly. Other design tools create pure binary programs. In general, design tools can speed up the design process, as well as offer better visual feedback.