Let's have a look at the ND. Like the Primary Flight Display (PFD) this is also a main instrument, this display is used for planning routes and navigating along these routes. This display also shows weather radar and EGPWS terrain map information.

In this overview I will explain only the ND of a B737-6/7/8/9 configured to our company's options.

First lets look at some of the older display systems for navigation. This next picture is of a HSI (Horizontal Situation Indicator).
Horizontal Situation Indicator
U can see that the basic concept of the HSI has a compass, a aircraft symbol, a deviation bar for the VOR and the VOR needle.

With the coming of the EFIS (Electronic Flight Instrument System) this HSI was replaced by a EHSI or Electronic Horizontal Situation Indicator.
Electronic Horizontal Situation Indicator
U can see that it is very similar to the HSI.

Boeing 737 next generations use the PFD (primary flight display) and ND (navigation display). The PFD replaces the EADI and the ND replaces the EHSI.
Here's a look at a Navigation Display.
Navigation Display
Once again, the Navigation Display is similar to the HSI and the EHSI.

The navigation display can be selected into different display modes, there is the plan mode, the map mode, the vor mode and the approach mode and (except for the PLAN mode) these modes can be selected to expanded (see previous picture) or the full rose mode (full compass rose) like this next picture.
full rose

This is the the APP mode. This mode is used for the Approach, it displays the ILS information (localiser glideslope.
APP mode

Here's the APP mode in full rose.
APP mode full rose

Then there is the VOR mode, this mode is used to display the VOR navigation data.
VOR mode

And the VOR mode again in the full rose mode.
VOR full rose

The VOR and the APP modes look at the VHF nav control panel. If a VOR frequency is tuned the system expects the ND not to be in the APP mode and when a ILS frequency is tuned the system expects the ND not to be in VOR mode.
If the wrong type frequency is tuned for the selected ND display, the crew will get the 'EFIS MODE/NAV FREQ DISAGREE' message.
Wrong frequency tuned

Then there is the MAP mode, this mode is used primarily by the flightcrew, this mode displays the FMC navigation, the heading, track, VNAV path, weather radar, EGPWS terrain and TCAS information.
MAP mode

The map mode again in the full rose mode.
Map mode in full rose

The flightcrew uses the plan mode wich may make it easier to enter a flightplan into the FMS (Flight Management System) because the screen in the PLAN mode is referenced to magnetic north and not to the aircraft heading. (In the PLAN mode the top of the screen represents magnetic north).
plan mode

The aircraft symbol is the one that we are in, it faces in the direction that the aircraft is facing and the selected waypoint is displayed in the center of the screen.
The PLAN mode can only be full rose, there is no expanded view for this mode.
aircraft symbol

Like the PFD the ND needs the I.R.S. input for compass heading and PPOS (present position).
If this input is not met the display will give a amber colored 'MAP' warning (warnings or cautions are displayed in amber or when they are really serious they can be displayed in red).
MAP warning
There is a TCAS FAIL warning on the left side of the screen, in this case this is because there is currently no way of displaying Resolution Advisories on the PFD due to the lacking of the attitude scale from the I.R.S. If the I.R.S.

I alligns the I.R.S. (setting it to ATT is enough for the TCAS to display attitude information but I need navigation for some more pictures).
U can see that there is still a TCAS caution but it changed from FAIL to OFF

Now let's have a look at the indications available to us.
First we have the aircraft itself, in the map, vor and app mode the aircraft symbol is displayed as a triangle with the top pointing at the current airplane heading (043 degrees magnetic heading as displayed in the top of the screen).
airplane symbol

Underneath the identifier u can see the DME (Distance Measurement Equipment) range to the VOR/DME station. In this case the distance to the ground station is 2.7 nautical miles
DME range

This is a map source identifier, when the I.R.S. is alligned the FMC can use the onboard systems (wichever are installed, GPS, Radio Nav, etc) to come up with a PPOS (present position). This present position is used to display the map (and remove the amber 'map' warning flag).
On aircraft with dual FMC's this indicator would indicate FMC 1 or FMC 2 wichever is used for the PPOS source.

Like the PFD, everything that is displayed in purple is a target situation, here, the purple bug is the selected heading.
selected heading

The flightcrew selects the heading on the MCP to indicate the flight director and/or autopilot what the MCP heading should be.
selected heading

Also displayd in purple is the flightplan. in this case this is a LOPIK SID but I will explain more about this later.

The flightplan is really a combination of seperate waypoints to reach a destination, the last visible waypoint in this example is point LOPIK wich is the end of a SID (Standard Instrument Departure).
A SID is a standard departure route to leave an airport in a certain direction to a certain point in space where the flightcrew can connect the rest of the flightplan onto.

here the EH084 is the next waypoint to be reached, EH represents Europe Holland.

This next one is the distance to the next waypoint in nautical miles.

This displays the calculated estimated time of arrival at the next waypoint.

In the top left corner we find information about GroundSpeed, in this case zero.

The True Airspeed.

The wind direction and speed.
wind direction and speed

The two white bars that the dotted line runs through is the runway that in this case we want to take off from. Right after the runway u can see the first waypoint at wich the crew should steer right to reach the second waypoint EH085.

The track line of the aircraft. (the triangle above the track line is the heading pointer).

There are 8 options to be selected on the EFIS control panel to display additional information on the Navigation Display.
These are the:
1- STA (station), displays all FMC data base navigation aids.
2- WPT (waypoint), displays all the waypoints in the FMS data base.
3- ARPT (airport), displays all the airports in the FMS nav data base.
4- DATA (yes... data), displays altitude constraint if there are any and the estimated time of arival for the waypoints.
5- POS (position) displays the GPS and IRS positions and bearing lines to VOR or ADF stations.
6- TFC (traffic) selects the TCAS system to display.
7- TERR (terrain) selects the map display of the EGPWS (Enhanced Ground Proximity System).
8- WXR (weather radar) selects the weather radar to on and automatically displays wxr information if the ND is in the MAP, VOR or APP mode.

First lets look at the STA (station) option wich displays all FMC data base navigation aids.
The hexagons are VOR beacons
The tripods are DME/TACAN's
The tripods with the extra lines are VORTAC's

The second option is the WPT (waypoint) option.
This option displays all the waypoints in the FMS data base.

Third we have the ARPT (airports) option.
This options displays all the airports in the FMS nav data base.

Fourth, we have the DATA option wich displays altitude constraint if there are any and the estimated time of arival for the waypoints.

Fifth we have the POS option, this displays the GPS and IRS position.
The white triangle indicates the aircraft PPOS (present position), i.e. the position the FMC uses to navigate.

Also in POS, the bearing to the selected VOR or ADF station is shown.

Sixth there is the TFC option, this selects the TCAS information on or off.
TCAS test

The seventh option is the TERR (terrain) option wich display of the EGPWS (Enhanced Ground Proximity System).
When the TERR option is selected on, the terrain database in the EGPWS computer compares the terrain altitude with the aircraft altitude, the different colors and dot densities indicate different levels of danger.

Here's the map display with the aircraft on the ground. Because the relative altitude between the aircraft and the terrain is now very small, the danger area spans almost across the entire cost.
If u look at where the black area meets the dotted area u can see the coastline.
(Google earth picture)

Then the eight option is the weather radar.This system displays weather conditions in different colors for different levels of hazard.
weather radar
This would indicate quite a hazardous area all around the aircraft but I took this picture with the aircraft in the hangar.
Also note the weather radar tilt in blue on the left side (WXR +2), the pitch of the dish can be selected on the WXR control panel and when the aircraft pitch changes, the weather radar compensates for that also by moving the radar dish up or down. For this the weather radar system needs I.R.S. information.

If a option is selected but there is too much information so that the display cannot display all of it, the amber 'EXCESS DATA' caution comes into view.
excess data

Another basic display are the VOR (VHF Omnidirectional Range) arrows. These arows display the direction to a VOR ground station. In this next picture both the VOR systems are tuned to 108.40 wich is schiphol airport. The VOR recognizes the ICAO (International Civil Aviation Organization) identifier and decodes this information to display the ICAO code of the airport: 'SPL' on the lower left and lower right parts of the screen for respectively VOR 1 and VOR 2.
VOR needles
The crew can use the VOR to fly towards a VOR station, intercept a VOR radial, non-precision approaches and radio navigation update (through FMS by combining a VOR with another VOR or a VOR with a DME or two or more DME's).

The VOR deviation bar. The white bar represents the selected course and the purple bar in the middle is the VOR deviation bar.
The flightcrew selects a course and if a selected VOR station is received the deviation bar will be in the middle of the course indicator if the aircraft is flying on the selected radial from the VOR station or 180 degrees in the other direction.
vor deviation

If the aircraft is flying 180 degrees in the other direction (for example flying 270 degrees heading on radial 90) the deviation bar will also be in the middle but the white triangle will indicate TO rather then FROM.
flying from the VOR station