How to read the band →
Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Porter
Porter has stayed fairly steady in American naming for generations. All-time it's been given to 21,801 U.S. babies, the 920th most common name by sound today, peaking at 921 in 2015, with 599 in 2025.
Porter has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).