# How to calculate how long an arc second is for a given long/lat?

I am wondering what area is covered by a dataset which is one arc second wide.

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Neither your title nor your body state clearly what you're after, and they even ask for different things. – Martin F Nov 16 '14 at 3:23

At sea level at the equator:

One degree of longitude is about 111km

One minute of longitude is one sixtieth of that: about 1.85km

One second of longitude is one sixtieth of that amount: about 31 meters or 100 feet.

However:

Arc-seconds of latitude remain nearly constant, while arc-seconds of longitude decrease in a trigonometric cosine-based fashion as one moves toward the earth's poles.

Arc seconds aren't really a great way to measure distance. Is there no possibility of using a ruler tool in your GIS or any kind of distance function?

Sources:

http://en.wikipedia.org/wiki/Arc_minute

http://www.esri.com/news/arcuser/0400/wdside.html

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Filled in some missing data -- hope you don't mind. – Martin F Nov 16 '14 at 3:34

1 milla náutica es un minuto de arco. En el Ecuador y a nivel del mar eso equivale a 1852m/60=30,86666667m

A 33,6º de latitud Sur cos 33º=0,83292 cos 33,6 * 30,866666667m = 25,709m por segundo de arco de longitud a esa latitud.

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Please translate to English for GIS-SE, thank you. – Mapperz Nov 16 '14 at 3:27

You might want to check out this page. Essentially, one degree longitude = 111km * cos(latitude)

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