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    <p>If you don't need to be very exact in your range, you can use an approximation to calculate the latitude and longitude ranges. Concept explained <a href="http://www.johndcook.com/blog/2009/04/27/converting-miles-to-degrees-longitude-or-latitude/" rel="noreferrer">here</a>:</p> <p>Using the city location and distance, find the change in latitude (this remains the same no matter where), and approximate change in longitude (varies based on latitude). Then calculate a bounding box.</p> <pre><code>import math # earth_radius = 3960.0 # for miles earth_radius = 6371.0 # for kms degrees_to_radians = math.pi/180.0 radians_to_degrees = 180.0/math.pi def change_in_latitude(distance): "Given a distance north, return the change in latitude." return (distance/earth_radius)*radians_to_degrees def change_in_longitude(latitude, distance): "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 (distance/r)*radians_to_degrees def bounding_box(latitude, longitude, distance): lat_change = change_in_latitude(distance) lat_max = latitude + lat_change lat_min = latitude - lat_change lon_change = change_in_longitude(latitude, distance) lon_max = longitude + lon_change lon_min = longitude - lon_change return (lon_max, lon_min, lat_max, lat_min) </code></pre> <p>To calculate events within distance <code>kms</code> of <code>city</code>:</p> <pre><code>lon_max, lon_min, lat_max, lat_min = bounding_box(city.lat, city.lon, kms) events = Event.objects.filter( city__lat__lte=lat_max, city__lat__gte=lat_min, city__lon__lte=lon_max, city__lon__gte=lon_min ) </code></pre> <p>Keep in mind that the error becomes larger with large distances, and the closer your are to the poles. There is also an issue with places near the anti-meridian (international date line), but that's easy to check for (check if longitude is > 180 or &lt; -180).</p> <p>If you want more acurate results, you can use this method as a first pass and then use your function, so you don't have to go through every event individually.</p>
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    1. POIt is necessary to use GeoDjango to query distances in Django?
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    1. POIt is necessary to use GeoDjango to query distances in Django?
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    1. COGreat answer! I understand the error thing. It's beacause the distance should be a round and this calculates a pseudo-rectangle, no? Anyway, i will use this method. If i note that the error is too much, i will switch to GeoDjango. Again, great answer and thanks!
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