Any model railroad, no matter how large, cannot possibly duplicate a prototype mile for mile. There are a variety of reasons why this is so, but probably the most important is that it would be plain boring. Not every scene along a railroad's right-of-way is scenically exciting or worth modeling. In order to achieve the best results, it is desirable to include only those scenes that would best describe your modeled prototype. The purpose is to capture the essence of the railroad in order to best represent it in modeled form, by selecting scenic elements that are interesting. This concept used in modeling a railroad is called "selective compression". It is, in its best form, the art of selecting and compressing the most representative scenes from your modeled prototype, making it fit in and work next to an other selected scene.
Lets take the example of a station platform that measures 100 feet in real life. In 1/29 this translates to approximately 42 inches. This sounds reasonable at first, but when you take into consideration the length of a 1/29 mainline steam locomotive (38 inches) and two passenger cars (32 inches each) for a total of 64 inches, you can quickly see how awkward this would be when modeled. Trying to model an engine service facility and small yard may take an area that is 4 feet wide by 22 feet long. A turntable in our scale could possibly be 3 feet or 4 feet in diameter. Try this is 1/20.3 and see how much more space is needed. In practice, we combine elements and compromise on the number of yard tracks that we build. Our sand, coal, and fuel servicing may be on one track rather than several, and the yard may be only three spurs. Selective compression assumes that there will be compromises, the extent of which will be determined by the amount of space that you have available.
When working with a garden layout you will have to accept compromises. While real railroads are point-to-point, we often build ours as a continuous loop since we like to see our trains run. In a point to point with maybe 21 feet of area to run, a switcher and several cars plus a caboose may be 6 feet long. This will be a short run, and not very satisfying for many of us. Thus our choice of the loop type track plan for our garden pikes.
With a garden layout, the greatest challenge is to make everything visually work together. As your train moves around the layout, what is really does is transition from scene to scene. Design for this concept by including scenic spots. Make it possible for the viewer to see your layout from different view points. Most important, try to set your planting and scenic features so that the whole layout cannot been seen from one location.
One of the most successful components of success in layout building is the phrase "Visual Integration". All visual elements should be kept to a common theme. You should have a corporate identity (either a real railroad or your own railroad name) for your railroad, and everything else should be of the same time period and geographic area that you are modeling. Structures should fit the scene, and railroad structures should have a "corporate" commonality. Weather everything based on the geographic area you are modeling (a lot of grime in the East and dust in the West). Run your trains at "prototypical speed" so that they slowly and believably progress through your layout.
If these concepts are followed, a very believable model of a prototype railroad can be created in miniature, which will greatly add to your personal satisfaction.