A schematic is a drawing of an item. In a sweater pattern, it is a drawing of the sweater with the dimensions of the sweater beside it. Not all sweater patterns include schematics, (and some folks don’t even look at them!) but they are a great tool for the knitter, and I highly recommend you include them. They don’t have to be fancy, just a faithful representation of the garment in a smaller 2-D scale. Beside the drawing, list the dimensions of the garment: the finished measurements. This way the knitter knows exactly what size it will be in all the points of the garment, and what shape it is at those points.
This is a great tool! Not only can the knitter follow along and check it as they work, but it is most helpful in choosing a size, seeing how the garment will work on your own body, and especially in choosing if you even want to knit it in the first place! This is so important. Can you knit it? Will it fit who it is intended for? Does its features match what you are looking for? These are all questions you need to answer before you begin, and I would argue, before you buy the pattern. Knitters love schematics, and use them long before they begin a project, as well as while they are working.
Many designers have told me that they don’t like to include the finished measurements or schematic on the product page where the pattern is sold, that they don’t want to share that information beyond the bust measurements, because it would be like ‘giving the pattern away for free.’ It most assuredly is not. The schematic and measurements are the dimensions of the item, in the same way the modeled pictures on the sales page demonstrate what the garment will look and fit like. They are not the whole pattern. They are not instructions, or stitch patterns, or increase and decrease rates, or design elements (minus some shaping clues). The knitter will want to buy your pattern even after studying your schematic.
Giving the knitter this information ahead of time will surely help you sell more patterns, not less, as an informed consumer is your best customer. We don’t want to hide things from the knitter then lose their future business when they purchase something that isn’t what they expected. Give the knitter the information they need upfront to know if your pattern is right for them, the same way they can look at and touch and feel clothes in a store or check fit and size charts when shopping ready-to-wear items online. This is why knitters study the photos so carefully before buying - they want to see all the details they can to see if they like what it will look like. Well, they want that same opportunity to look closely at whether it will fit how they like! The schematic and the finished measurements are how they will know if the fit will be appropriate for them or for whomever it is intended.
The more information you can give your knitter about what they are buying, the more they will appreciate your efforts and like buying from you. Don’t we all want to know exactly what we are buying, what we are getting into? That’s why we read reviews and ask questions and find out all we can, so we know what we are getting. Not being able to know the measurements of a garment you are going to make to fit someone is like going in completely blind and not even knowing if you can make it at all. There is nothing more frustrating than buying a pattern and then realizing it won’t work at all for your needs, or that it will work but not how you thought, and you are unprepared. Who wants that?
Share your schematic and finished measurements with your knitter before they buy. Give them all the information they need to be able to ascertain fit and choose a size. They will thank you (and it will make things better for you too!).