Use EasyMapMaker to export your visible map to a poster sized image. Poster size maps can be generated as large as 10800x7200 pixels (3 feet x 2 feet at 300 dpi). The image generator has produced images as large as 14400x10800 (4 feet x 3 feet) and is capable of producing larger images (more to come on this).
A live map url is something similar to https://www.easymapmaker.com/map/9a804fec8c754bf7cd9f4bc435fafb14
High resolution image generation (and all image generation besides the visible map option) uses the zoom level and resolution of the map. This means areas outside of the map will show up on the generated image. For example, in the modal/popup below the visible map is 4556 x 1696 pixels in the popup. A 10800 x 7200 image will grab over 2500 pixels from the top and the bottom (7200 - 1696 = 5504 pixels not shown) of the map that are not visible. Zooming in 2 levels would do a better job of revealing the total height of the image that will be generated (4 * 1696 = 6784 pixels, a few pixels less than the actual height of the image generated).