def _is_coordinate(value):
    """Return True if the string value contains a coordinate."""
    if len(value) <= 0:
        return False
    if value.startswith(('+', '-')):
        value = value[1:]
    count = value.count('.')
    if count <= 0:
        return value.isdigit()
    if count == 1:
        return value.replace('.', '').isdigit()
    return False