I’ll try to keep this simple…If I draw a simple rectangle, that rectangle will subdivide into many pieces during the design-Process. Question; Why, and how can this be prevented? Thanks.
That’s actually a pretty vague question. There are many things that could cause it to be subdivided. Maybe you could supply a .skp file that shows the subdivision you’re referring to.
What version of SketchUp are you actually using? Your profile says SketchUp Make (without a year) but you posted in the SketchUp for Web category.
Any time that an edge has another edge join it somewhere between the endpoints, the first edge will become two edges.
If there a reason that matters, and if you’re using the web version, you can select the separate edges, right-click, and choose Weld Edges. That will recombine them into one curve.
I’m also not sure what exactly you mean, but I’ll add to colin’s suggestion of welding edges… You can also group the geometry to create a new single rectangle group. Whether you weld the edges or not. Or similarly, make it a component. A component is a group with extra features. Then, if you double-click that group/component, you will enter its context and can edit its parts – i.e. its 4 edges and 1 face.
Most advanced users will tell you that grouping is essential to their workflow. For easy grouping, double-click or triple-click an entity (face or edge) to select connected entities.
Here is a picture of the floor. It started out a single piece, and over time it kept subdividing into what you see in the picture. That’s why I tried to "Keep the explanation simple, because it happens to any shape. Oh, I’m using Sketchup Make 2017…
Generally that sort of thing happens when the geometry gets distorted. SketchUp is trying to maintain faces so it creates triangulation. You can try erasing those edges. If the faces disappear, too, the faces aren’t in the same plane. Using groups and components to prevent mergers of geometry can help. If you share the .skp file we can tell you more about what’s happening and how to prevent it.
Without seeing the model it is impossible to say, but probably you have moved points without noticing.
Is the model far from the origin?