Given names (first names) and names of places have a long history of cross-fertilization. Places have been named after the people who lived there, and people in turn may be named (or at least nicknamed) after the places they live. Some names have cycled through the process more than once!
Taking a peek at the naming patterns
Given names that are taken from place names or the names of natural features turn the usual naming pattern on its head. Instead of girls getting all the fun, this group of names is more often given to boys. The reason is simple: Most of these names first turned into family surnames, and the practice of turning surnames into given names has traditionally benefited boys more than girls.
There are exceptions to this pattern. Names of countries are often considered feminine (or at least often look feminine). So names like India and China tend to skip the surname step and go straight to being girls' names. Even when the name doesn't end with that telltale "a," a country name like Brittany is more likely to enter the field as a girl's name.
Names from descriptions of natural features like Cliff, Rock, or Glen may be taken from surnames, but just as often they may be given for the image of strength and ruggedness they project.
More recent place-name borrowings may follow more than one rule. Sierra (mountain) may be given to boys as a natural feature and be given to girls because of the "a" at the end of the word.
In some cases, a given name may be identical to a place name without having a direct connection. Paris, as a girl's name, is most likely inspired by the glamorous city, but as a boy's name it connects historically with the Paris of Greek mythology. Florence (whether for boys or girls) comes from an old Roman family name rather than from the city.
Taking your proper places
Proper names of places usually refer to a specific location. Generally they start out as surnames for families that lived in those places and only later are taken up as given names. In some cases, though, these names started out as personal names that were later used to name locations.
ALTON: (m) English; various origins such as "old town," or "Alf's town". The name is not well known, although it enjoyed a rather steady mild popularity throughout the early part of the 20th century. Alton Locke is the hero of Charles Kingsley's novel by that name. Alton Brown is the host of a popular cooking show called "Good Eats."
ASHTON: (f, m) English; ash tree town. The name became suddenly popular for both boys and girls in equal numbers starting in the '80s, but in an unusual twist, the male popularity continued rising while the female use has dropped (perhaps diverted to ASHLEY and ASHLYN). Just as there is a general pattern of names ending in "-ley" becoming girls' names, names ending in "-ton" (or in "n" in general) seem to be associated more with boys. Bearers include actor Ashton Kutcher and early horror fiction writer Clark Ashton Smith. Variant: (f) Ashtyn.
ASIA: (f) Greek; East, where the sun rises. Continent names are rare as given names, despite the fact that continents have always been personified as female (as in the Greek legend of Europa and the bull). This name has become popular in the last couple of decades. Bearers include Italian actress Asia Argento.
BLAIR: (f, m) Gaelic; a plain, a field. Unlike many place names, this increases in popularity for boys through the 20th century. The feminine name has had some small popularity in recent decades. The timing isn't right for the horror film The Blair Witch Project to be responsible, but a character of this name on the TV show The Facts of Life is more likely.
BRADLEY: (m) English; broad meadow. Like most place-based surnames, this began with occasional use in the nineteenth century. Charles Dickens gave the name to the character Bradley Headstone in Our Mutual Friend. The significant boost of popularity the name saw in the '50s and later may have been partly in honor of World War II general Omar N. Bradley, but the name was also swept up in the general fashion for boys' names beginning with "Br-" and continues in high popularity through the end of the century. Variant: Bradly. Diminutive: Brad.
BRITTANY: (f) English; the English name for the region of Brittany in northern France. The origin is the same as the name Britain. The name first hits the charts in the '70s and explodes in popularity, reaching number 6 in the '90s. Pop singer Britney Spears rides the wave but doesn't seem to have caused it. Like the other popular late-century names starting with "Br-" this seems to have been the right sound at the right time. Variants: Britany, Britney, Britni, Britny, Brittaney, Brittani, Brittanie, Brittany, Brittnee, Brittney, Brittni, Brittnie, and Brittny.
Featuring the natural world in names
While proper place names usually refer to a specific location, words for natural features are more generic and refer to an entire class of locations. As surnames, they often arose to distinguish neighbors: John who lives at the ford rather than John who lives by the meadow. But these given names may also be taken directly from the ordinary words, rather than from surnames.
MEADOW: (f) English; a meadow, a grassy field. The name has begun being used as a given name only recently. It's the name of the daughter in the TV show The Sopranos.
RIDGE: (m) English; a ridge, a line of sharp hills. The name has shown up very rarely in the last decade or so. This and the following RIVER may be rare cases of taking boy's names directly from ordinary words.
RIVER: (m) English; a river, a water-course. The name has had increasing popularity only in the last couple of decades. One likely source of inspiration has been actor River Phoenix.
ROCK: (m) English; a rock, a stone. This name may be in the current category under false pretenses and instead be an Englishing of the Italian name Rocco. Both Rock and Rocky became popular just as Rocco faded in the mid-twentieth century. The name of movie star Rock Hudson was direct from the stone, however, being one of those Hollywood publicist's inventions. Pro wrestler turned-actor "The Rock" (real name: Dwayne Johnson) is as solid as his nickname implies. Variant: Rocco and Rocky.
SIERRA: (f) Spanish; a mountain range. This name shows up abruptly in the '80s and climbs the charts rapidly. Sierra has a strong outdoorsy feel, not simply from the meaning, but from association with the environmentalist Sierra Club. Variants: Ciarra, Ciera, and Cierra.
WADE: (m) English; a ford, a place where you can wade. The name has been consistently popular throughout the 20th century. There is a minor character in Gone With the Wind named Wade, where it is said he was named after the surname of his father's commanding officer.