Whether a large banner has a seam depends on the size of the banner.
In general most all large banner prints won't have a seam, or banner printing in general, unless you are looking at an extremely large billboard-sized banner. When manufacturing a large banner we first start with the banner printing material itself, like vinyl banner material or mesh banner material (which is also a vinyl banner material that is perforated in nature.) Our banner printing materials range in size from 2 feet in height up to 16 feet in height and come on rolls that range in length from 25 yards to 100 yards.
But the height of each individual banner material roll is heavily dictated by banner material weight and banner material color choice. What this means is we stock a wide range of banner material for printing large banners in different weights (for example: 10 oz. , 13 oz. 16 oz., etc.) that come in a variety of colors like standard colors even including fluorescent colored banner material choices. Some banner material weights only come on rolls up to 6 feet tall, while different banner weights are available on rolls measuring up to 16 feet tall.
For instance, if you needed a 10 foot tall banner printed on orange fluorescent banner material your banner would have a seam. The reason for the large banner seam would be because our fluorescent banner material rolls max out at 6 feet in height. So once the 6 foot height cap of the original banner material was hit more fluorescent banner material would need to be added to the top, thus creating a seam, when the two pieces are sewn together to achieve the desired 10 foot banner height requirement.
But on the other hand, if you needed a large 10 foot full color printed banner you wouldn't encounter a large banner seam. This is because we could print your large banner on our 16 oz. white vinyl banner material that comes on a 16 foot banner roll. The banner would be printed and the extra material would be cut away leaving enough material to create a nicely stitched hem.
So essentially, if you need a very large banner without a seam, it can most likely be done (depending on a few specific other banner needs.) And while a 16 foot tall banner should just about cover the largest banner needs, if your banner requires a larger height, then the banner will need to be seamed together to meet your requirements.