Need Help: Calculating nearest location distance and location ID

Shailesh2thakur distance is in km. To switch to miles change Earth radius parameter in code accordingly. 

let
    sites = your_SiteMaster_table,
    vehicles = your_Parking_table,
// add geo record into vehicles table
    v_geo = Table.AddColumn(vehicles, "geo", each GeographyPoint.From(Number.From([long]), Number.From([lat]))),
// transform sites table into list of records with geo coordinates
    sg = List.Buffer(
        Table.ToList(
            sites,
            (x) => GeographyPoint.From(Number.From(x{2}), Number.From(x{1})) & [site = x{0}]
        )
    ),
// distance calculation function
    distance = (parking) => (site) =>
        [r = 6371, // this is Earth radius in km. Change to miles if you like
        p = Number.PI / 180,
        a = 0.5 - 
            Number.Cos( (site[Latitude] - parking[Latitude]) * p) / 2 +
            Number.Cos(parking[Latitude] * p) * 
                Number.Cos(site[Latitude] * p) *
                    (1 - Number.Cos( (site[Longitude] - parking[Longitude]) * p)) / 2,
        d = 2 * r * Number.Asin(Number.Sqrt(a))][d],
// this function finds closest site and distance to it
    closest = (v) =>
        [f = distance(v),
        m = List.Min(sg, null, f),
        dist = m & [distance = distance(v)(m)]][dist],
// now we apply closest function to "geo" column with locations
    find_closest_sites = Table.TransformColumns(v_geo, {"geo", (x) => closest(x)}),
// and finally expand site ID and distance to it
    expand_site_info = Table.ExpandRecordColumn(find_closest_sites, "geo", {"site", "distance"})
in
    expand_site_info