Poor VFR navigation technique can result in an airspace infringement. One of the most common ways to navigate under VFR is by selecting, during the pre-flight briefing, ground features which are marked on the VFR navigation maps and then looking for them on the ground during the flight. These VFR navigation maps depict topographic features and other information of interest to pilots flying visually, including major landmarks, terrain elevations, visual navigation routes, ground-based navigation aids, airports, rivers, cities, and airspace boundaries.
VFR Map features
There are three basic types of features on a map:
Point - used to show objects that are considered as one point (e.g. peaks, towers, etc.). Objects are usually represented by special symbols.
Line - used to show objects that are considered 1-D, i.e. only have length (e.g. roads, rivers, coastlines, etc.)
Area - used to show large 2-D objects with their contours (e.g. lakes, cities, etc.)
Line Features Specifics and Benefits
Line features can be very helpful in VFR navigation because:
They are easy to spot (unlike point features) and identify. This is especially true when orientation is lost. In many cases the easiest way to re-establish position awareness is spotting a coastline, if one is available.
They are easy to follow (unlike point and area features). Flying along a line feature can often offer high level of position certainty at the price of slight increase of track distance.
The intersection points between two line features can be used as turning points. Also, using such spots is an easy and accurate way to determine one’s position.
It is usually easier to find unique line features on a map and recognize them from the cockpit. Also, line feature curves offer good precision when determining the aircraft position. By contrast, area features are often too large to offer precise position reading and point features can be ambiguous.
Line Feature Use Considerations
Although line features usually make orientation and navigation easier, there are several issues that need to be considered:
A line feature which looks good on a map may not be easy to locate from the air due to other terrain features. Therefore suitable line features need to be chosen during flight preparation.
Line features are generally unique but can still be mistaken depending on the circumstances (e.g. two straight power lines). The map should be examined to address this issue and make sure the right feature is identified when airborne. Check that the line feature has the same compass bearing as the one on your map - are you following the right one?
Line features are best followed when there is a gap between the track and the feature (e.g. flying on a parallel track that allows constant observation of the feature).
Observation of line features can be a useful way of staying clear of controlled airspace.
Maintain a good lookout for other aircraft navigating using the same line feature.