A quick look on how index look-ups work

A quick look on how index look-ups work db.cities.find( { population: { $gte: 2000000 }, elevation: { $gte: 1654 } } );

⇒	...	...	...
	Shijiazhuang	1992474	77
	Medellín	1999979	1500
	Almaty	2000900	793
	Zhengzhou	2014125	104
	Al Başrat al Qadīmah	2015483	6
	Kowloon	2019533	92
	Johannesburg	2026469	1767
	Dalian	2035307	33
	...	...	...

%n = 0 - nscanned = 0%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
⇒	Almaty	2000900	793
	Zhengzhou	2014125	104
	Al Başrat al Qadīmah	2015483	6
	Kowloon	2019533	92
	Johannesburg	2026469	1767
	Dalian	2035307	33
	...	...	...

%n = 0 - nscanned = 0%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
	\|ff7777\|Almaty\|	\|ff7777\|2000900\|	\|ff7777\|793\|
⇒	Zhengzhou	2014125	104
	Al Başrat al Qadīmah	2015483	6
	Kowloon	2019533	92
	Johannesburg	2026469	1767
	Dalian	2035307	33
	...	...	...

%n = 0 - nscanned = 1%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
	\|ff7777\|Almaty\|	\|ff7777\|2000900\|	\|ff7777\|793\|
	\|ff7777\|Zhengzhou\|	\|ff7777\|2014125\|	\|ff7777\|104\|
⇒	Al Başrat al Qadīmah	2015483	6
	Kowloon	2019533	92
	Johannesburg	2026469	1767
	Dalian	2035307	33
	...	...	...

%n = 0 - nscanned = 2%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
	\|ff7777\|Almaty\|	\|ff7777\|2000900\|	\|ff7777\|793\|
	\|ff7777\|Zhengzhou\|	\|ff7777\|2014125\|	\|ff7777\|104\|
	\|ff7777\|Al Başrat al Qadīmah\|	\|ff7777\|2015483\|	\|ff7777\|6\|
⇒	Kowloon	2019533	92
	Johannesburg	2026469	1767
	Dalian	2035307	33
	...	...	...

%n = 0 - nscanned = 3%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
	\|ff7777\|Almaty\|	\|ff7777\|2000900\|	\|ff7777\|793\|
	\|ff7777\|Zhengzhou\|	\|ff7777\|2014125\|	\|ff7777\|104\|
	\|ff7777\|Al Başrat al Qadīmah\|	\|ff7777\|2015483\|	\|ff7777\|6\|
	\|ff7777\|Kowloon\|	\|ff7777\|2019533\|	\|ff7777\|92\|
⇒	Johannesburg	2026469	1767
	Dalian	2035307	33
	...	...	...

%n = 0 - nscanned = 4%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
	\|ff7777\|Almaty\|	\|ff7777\|2000900\|	\|ff7777\|793\|
	\|ff7777\|Zhengzhou\|	\|ff7777\|2014125\|	\|ff7777\|104\|
	\|ff7777\|Al Başrat al Qadīmah\|	\|ff7777\|2015483\|	\|ff7777\|6\|
	\|ff7777\|Kowloon\|	\|ff7777\|2019533\|	\|ff7777\|92\|
	\|77ff77\|Johannesburg\|	\|77ff77\|2026469\|	\|77ff77\|1767\|
⇒	Dalian	2035307	33
	...	...	...

%n = 1 - nscanned = 5%

	...	...	...
	\|777777\|Shijiazhuang\|	\|777777\|1992474\|	\|777777\|77\|
	\|777777\|Medellín\|	\|777777\|1999979\|	\|777777\|1500\|
	\|ff7777\|Almaty\|	\|ff7777\|2000900\|	\|ff7777\|793\|
	\|ff7777\|Zhengzhou\|	\|ff7777\|2014125\|	\|ff7777\|104\|
	\|ff7777\|Al Başrat al Qadīmah\|	\|ff7777\|2015483\|	\|ff7777\|6\|
	\|ff7777\|Kowloon\|	\|ff7777\|2019533\|	\|ff7777\|92\|
	\|77ff77\|Johannesburg\|	\|77ff77\|2026469\|	\|77ff77\|1767\|
	\|ff7777\|Dalian\|	\|ff7777\|2035307\|	\|ff7777\|33\|
⇒	...	...	...

%n = 1 - nscanned = 6%