The game is based off of that.
Also, this may seem silly, but how does one draw large pixelated images without doing everything pixel by pixel. I found some good pixel art programs like Piq, but it only makes small images.
make the image the exact size you want the grid to be
then, for example, if you want one pixel to be 8x, scale the image using Nearest Neighbor to 100 * 8 (800%)
most editors have something like this