def create_buffer(gdf,buffer_distance):
    """
    This function is used to create buffer around given geodataframe with a specified distance
        Input:
            - gdf: input geo dataframe
        Output: 
            - buffer_poly: a buffer around the input gdf with the specified distance
    """
    buffer_poly = gdf.copy()
    buffer_poly["geometry"]=gdf.geometry.buffer(buffer_distance)
    return buffer_poly