In[]:=
​​latlong=Table[{RandomReal[{-80,80}],RandomReal[{-180,180}]},{1000}];​​tab1=ToTabular[latlong,"Rows",<|"ColumnKeys"->{"lat","long"}|>];​​tab2=ToTabular[Map[{GeoPosition[#]}&,latlong],"Rows",<|"ColumnKeys"->{"geo"}|>];​​{tab1,tab2}
Out[]=

Tabular
Row count: 1000
Column count: 2

,
Tabular
Row count: 1000
Column count: 1


In[]:=
N[ByteCount[tab2]/ByteCount[tab1]]
Out[]=
10.5843