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I used the following code from this github repo I know it take a point coodinates and return area of 10 sequare Km around it by transforming Km to degree, but I need to make this area to 5 sequare Km for example. how can I achieve that? The only number I found is (3.75) but I'm not sure what it represents and how to change it to get the area I need. I know this might sound obvious for some, but I have zero background in GIS and GEO data and I played around with the code but the results I had didn't make any sense at least for me.

import math

# Distances are measured in kilometers.
# Longitudes and latitudes are measured in degrees.
# Earth is assumed to be perfectly spherical.

earth_radius = 6271.0
degrees_to_radians = math.pi/180.0
radians_to_degrees = 180.0/math.pi

def change_in_latitude(kms):
    "Given a distance north, return the change in latitude."
    return (kms/earth_radius)*radians_to_degrees

def change_in_longitude(latitude, kms):
    "Given a latitude and a distance west, return the change in longitude."
    # Find the radius of a circle around the earth at given latitude.
    r = earth_radius*math.cos(latitude*degrees_to_radians)
    return (kms/r)*radians_to_degrees

def ten_km_square(latitude, longitude):
    slat, nlat = latitude+change_in_latitude(-3.75), latitude+change_in_latitude(3.75)
    wlon = longitude+change_in_longitude(latitude,-3.75)
    elon = longitude+change_in_longitude(latitude, 3.75)
    return(nlat, wlon, slat, elon)

def main(lon, lat):
    '''First argument degrees longitude (E is positive, W negative)
        of the landslide location,
        second argument latitude (N positive, S negative),
        in decimal format(not minutes etc.)'''
    nlat, wlon, slat, elon = ten_km_square(lat,lon)
    #print("(NLat:{:.4f},WLon:{:.4f}),(SLat:{:.4f},ELon:{:.4f});".format(nlat, wlon, slat, elon))
    print("var region = '[[{:.4f},{:.4f}], [{:.4f},{:.4f}], [{:.4f},{:.4f}], [{:.4f},{:.4f}]]';".format(wlon,nlat,elon,nlat,wlon,slat,elon,slat))
    print("var rectangle = [{:.4f},{:.4f},{:.4f},{:.4f}];".format(wlon,slat,elon,nlat))

#change these to longitude, latitude
main(18.07769,44.14354)
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  • This definitely doesn't make a 10km² square or a square with 10km sides However it does make a square with ~7.5 km (3.75*2) sides and an area of ~58km² (7.5²)
    – Kalak
    Commented Aug 26, 2020 at 6:39

1 Answer 1

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Using the code you provided, to get a ~5km² square area you would need a value of 1.118 km instead of 3.75 km

sqrt(5) ~= 2.236 (side of square) / 2 = 1.118 km

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  • Thank you! I'm planning to read more about the subject and have a better understanding on how it is calculated :)
    – salRad
    Commented Aug 26, 2020 at 8:57

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