📚 Bearings and Scale Drawings | 方位角与比例图
Bearings and scale drawings are essential tools for describing direction and distance on maps. This article covers how to measure, draw and calculate bearings, how to read and use scale drawings, and how to apply both skills to real-world navigation problems.
方位角和比例图是地图上描述方向和距离的重要工具。本文讲解如何测量、绘制和计算方位角，如何阅读和使用比例图，以及如何将这两种技能用于实际的导航问题。
1. What Are Bearings? | 什么是方位角？
A bearing is a direction measured from the north line in a clockwise direction. It tells us the direction of one point from another. The angle is written with three digits, so north-east is 045°, east is 090°, south is 180° and west is 270°.
方位角是从正北线沿顺时针方向测量的方向角。它表示一个点相对于另一个点的方向。角度写成三位数，因此东北方向为 045°，正东为 090°，正南为 180°，正西为 270°。
| Direction | Bearing | 中文方向 |
|---|---|---|
| North | 000° | 北 |
| East | 090° | 东 |
| South | 180° | 南 |
| West | 270° | 西 |
2. Key Rules for Bearings | 方位角的关键规则
Always measure a bearing clockwise from north. Use three digits at all times. A bearing of 0° is written 000°, and 12° is written 012°. Bearings are never negative and cannot exceed 360°.
方位角总是从正北按顺时针方向测量。始终使用三位数字书写。0° 写作 000°，12° 写作 012°。方位角没有负数，也不能超过 360°。
Common bearings include north-east 045°, south-east 135°, south-west 225° and north-west 315°. These are often tested in checkpoint questions because they link compass directions with angles.
常见方位角包括东北 045°、东南 135°、西南 225° 和西北 315°。这些经常出现在 Checkpoint 考题中，因为它们将罗盘方向与角度联系起来。
3. Measuring a Bearing on a Diagram | 在图上量测方位角
To measure a bearing between two points on a diagram, first join the two points with a straight line. Draw a north line at the starting point. Place the protractor so that its centre is on the starting point and 0° points north. Read the angle clockwise from north to the line.
要测量图上两点之间的方位角，先用直线连接两点。在起点处画一条正北线。将量角器中心放在起点，并使 0° 指向北方。按顺时针方向读出从北到这条直线的角度。
If a line points exactly to the right of north, the bearing is 090°. If it points halfway between north and east, the bearing is 045°. If it points halfway between east and south, the bearing is 135°.
如果一条线指向正北右侧，方位角是 090°。如果它指向北和东的中间，方位角是 045°。如果它指向东和南的中间，方位角是 135°。
4. Drawing a Bearing | 绘制方位角
To draw a bearing from a point, draw a north line upward. Place the protractor centre at the point with 0° on north. Mark the required angle clockwise. Remove the protractor and draw a straight line through the point and your mark. Label the bearing with three digits.
要从一个点绘制方位角，先向上画正北线。将量角器中心放在该点，使 0° 对准北方。按顺时针标出所需角度。移开量角器，画一条经过该点和标记的直线。用三位数标注方位角。
For example, to draw a bearing of 075° from point P, place the protractor with its centre on P, locate 075° clockwise from north, mark it, and draw the line from P through the mark. This line shows the required direction.
例如，要从点 P 绘制 075° 的方位角，将量角器中心放在 P 上，从正北顺时针找到 075°，做标记，然后从 P 画出经过该标记的直线。这条线就表示所需方向。
5. Back Bearings | 反向方位角
A back bearing is the direction from the second point back to the first. To find it, add 180° if the original bearing is less than 180°, or subtract 180° if the original bearing is 180° or more.
反向方位角是从第二个点返回到第一个点的方向。如果原方位角小于 180°，则加上 180°；如果原方位角大于或等于 180°，则减去 180°。
Back bearing = B + 180° if B < 180°
反向方位角 = B + 180°（当 B < 180°）
Back bearing = B − 180° if B ≥ 180°
反向方位角 = B − 180°（当 B ≥ 180°）
= 245°. If the bearing of B from A is 210°, the bearing of A from B is 210° − 180° = 030°.
如果从 P 到 Q 的方位角是 065°，那么从 Q 到 P 的方位角是 065° + 180° = 245°。如果从 A 到 B 的方位角是 210°，那么从 B 到 A 的方位角是 210° − 180° = 030°。
6. Scale Drawings | 比例图
A scale drawing represents a real shape or place at a smaller or larger size. The scale is usually written as a ratio or as a statement. For example, a scale of 1:50000 means 1 cm on the map represents 50000 cm in real life, which is 0.5 km.
比例图以缩小或放大的尺寸表示真实物体或地点。比例尺通常写成比或说明文字。例如，1:50000 表示图上 1 厘米代表实际 50000 厘米，也就是 0.5 公里。
| Scale statement | Ratio | Meaning |
|---|---|---|
| 1 cm to 1 m | 1:100 | 1 cm on map = 100 cm in real life |
| 1 cm to 5 km | 1:500000 | 1 cm on map = 5 km in real life |
