Plotting and Measuring on Charts

Tools and Techniques for Plotting on Charts

Plotting on aviation charts involves marking positions, drawing tracks, and measuring distances using standard navigation tools. Dividers or a marked edge of paper are commonly used to measure distances, which are then compared to the chart's scale (often found at the top or bottom of the chart) to convert chart units to nautical miles. Protractors or the chart's graticule help measure and plot bearings and tracks.

Measuring Distance on Navigation Charts

To measure a distance between two points, place your dividers or a straight edge between them, then transfer that span to the chart's distance scale. Always use the scale closest to the latitude of the segment, as scale can vary with chart projection. For example, on a Lambert conformal chart, the scale is most accurate at the standard parallels and varies slightly away from them.

Plotting Bearings and Tracks

To plot a bearing (such as from an NDB or VOR), use the chart's compass rose or a protractor to draw the line from the relevant navigation aid. When plotting a track between two points, ensure you account for the chart projection—Lambert charts allow straight lines to approximate great circles, while polar stereographic charts are used for high-latitude routes.

Fixing Positions with Radio Aids

Position fixing is achieved by plotting bearings from two or more radio navigation aids (e.g., VOR, DME). The intersection of these lines provides an accurate aircraft fix, which is essential for en-route navigation and cross-checking against estimated positions.

Chart Projections and Scale Variations

Different chart projections (Lambert, Mercator, Polar Stereographic) affect how tracks and distances are plotted. The scale on a Lambert chart is true at the standard parallels and changes slightly elsewhere, but within the parallels, the variation is less than 1%. Understanding these variations is key for accurate plotting and measurement.

Standard Plotting Symbols

Using conventional plotting symbols (e.g., circles for fixes, arrows for tracks) ensures clarity and consistency, both in training and operational environments. Always use pencil on original charts to allow corrections and preserve the chart for future use.