📚 Year 7 OCR Geography: Quick Reference Formulas & Principles | Year 7 OCR 地理：公式定理速查手册
This quick reference guide brings together the most important formulas, calculations and key principles you will encounter in Year 7 OCR Geography. From map skills to population change, and from climate graphs to river processes, having these tools at your fingertips will help you answer questions with confidence.
这份速查手册汇集了你在 Year 7 OCR 地理课程中会遇到的最重要公式、计算方法和关键定理。从地图技能到人口变化，从气候图表到河流作用，随时查阅这些工具能帮助你自信地解答问题。
1. Map Scale: Converting Map to Real Distance | 地图比例尺：图上距离与实际距离的转换
Scale tells you how much the real world has been reduced to fit on a map. It is usually written in three ways: as a statement (1 cm to 1 km), as a ratio (1:100,000), or as a scale bar. To find the real ground distance, multiply the measured map distance by the scale factor.
比例尺告诉你真实世界缩小了多少才能放进地图。它通常有三种表示方式：文字说明（如 1 厘米代表 1 公里）、数字比例尺（如 1:100,000）或比例尺条。要计算实际地面距离，用图上测量的距离乘以比例尺倍数。
- Measured map distance (cm) × scale denominator ÷ 100,000 = distance in km (for a typical OS map using 1:50,000) — 图上测量的距离（厘米）× 比例尺分母 ÷ 100,000 = 公里数（典型的 1:50,000 地形图）
- Always convert units carefully: 100 cm = 1 m, 1000 m = 1 km — 务必仔细换算单位：100 厘米 = 1 米，1000 米 = 1 公里
2. Straight‑line Distance on a Map | 地图上的直线距离
Place the straight edge of a piece of paper between the two points. Mark the start and end on the paper, then place the paper against the scale bar. Read the distance directly. If using a ratio scale, measure in centimetres and apply the scale calculation.
将一张纸的直边对齐两个点，在纸上标记起点和终点，然后把纸贴到比例尺条上直接读出距离。如果使用数字比例尺，就以厘米为单位测量并应用比例尺公式计算。
- Distance = measured length (cm) × map scale factor — 距离 = 测量长度（厘米） × 地图比例尺倍数
- Keep units consistent — 保持单位一致
3. Curved Distance: Measuring Roads and Rivers | 曲线距离：道路与河流的测量
Use a piece of string or the edge of a paper strip. Lay it along the curve, mark the end point, then straighten it against the scale bar. Alternatively, use a map measurer (opisometer) and read the dial. This technique is essential for following meandering features.
用一根细绳或纸条边缘沿着曲线摆放，标记终点，再将其拉直对齐比例尺条。也可以使用曲线计（描图计）读取刻度盘。这一技巧对追踪蜿蜒的河流和道路非常关键。
- Total curved distance = straight‑line equivalent measured against scale — 曲线总距离 = 对齐比例尺后测出的等效直线长度
4. Area on a Map: Regular and Irregular Shapes | 地图上的面积：规则与不规则形状
For a rectangle or square, multiply length by width using scaled distances. For irregular shapes, use grid squares: count full squares, then add half the number of part squares. Each grid square represents a known area on the ground (e.g. 1 km² if the grid is 1 cm on a 1:50,000 map).
对于矩形或正方形，用比例尺换算后的长度乘以宽度。对于不规则形状，使用网格法：先数出完整的网格，再把不完整网格的数量除以 2 加总。每个网格代表地面上已知的面积（例如在 1:50,000 地图上，1 厘米网格为 1 平方公里）。
- Area (km²) ≈ (full squares + ½ partial squares) × area per grid square — 面积（平方公里）≈（完整网格数 + ½ 不完整网格数）× 每个网格代表的面积
5. Gradient: Measuring Slope Steepness | 坡度：测量坡面陡峭程度
Gradient compares the vertical rise to the horizontal distance. It is often expressed as a ratio (1:10) or as a fraction. The formula is: Gradient = vertical interval (height difference) ÷ horizontal distance. Use contour lines to find the vertical interval.
坡度比较的是垂直上升高度与水平距离。通常用比例（1:10）或分数表示。公式为：坡度 = 垂直高差 ÷ 水平距离。利用等高线获取垂直高差。
Gradient = vertical rise ÷ horizontal distance
- Example: a 50 m rise over 500 m gives 50 ÷ 500 = 0.1 or 1:10 — 例如：50 米高差，水平距离 500 米，50 ÷ 500 = 0.1，即 1:10
6. Grid References: 4‑figure and 6‑figure Accuracy | 网格坐标：四位与六位精准定位
A 4‑figure grid reference locates a grid square (e.g. 4521), while a 6‑figure reference locates a specific point within that square (e.g. 453219). Always read ‘along the corridor and up the stairs’ (eastings first, then northings).
四位数网格坐标定位一个网格方格（例如 4521），而六位数坐标则定位方格内的具体一点（例如 453219）。始终遵循“先向东走再向北走”的原则（先读东距，再读北距）。
- 4‑figure: easting (two digits) + northing (two digits) = square — 四位数：东距（两位）+ 北距（两位）= 方格
- 6‑figure: divide square into tenths; add a digit for easting position and a digit for northing position — 六位数：将方格十分之；增加一位东距定位数和一位北距定位数
7. Population Density: How Crowded a Place Is | 人口密度：一个地方有多拥挤
Population density describes the number of people living per unit of area, usually per km². It helps to compare how crowded different regions are. High density figures appear in urban areas, low density in rural or mountainous zones.
人口密度描述单位面积上居住的人数，通常以每平方公里人数计。这有助于比较不同区域的拥挤程度。城市地区人口密度高，农村或山区则较低。
Population Density = total population ÷ total land area (km²)
- Example: 5000 people in 25 km² → 5000 ÷ 25 = 200 people per km² — 例：5000 人生活在 25 平方公里 → 5000 ÷ 25 = 200 人/平方公里
8. Birth Rate, Death Rate and Natural Increase | 出生率、死亡率与自然增长
These measures show how a population changes without migration. Birth rate is the number of live births per 1000 people per year. Death rate is the number of deaths per 1000 people per year. Natural increase is the difference between them.
这些指标展示在没有移民的情况下人口如何变化。出生率是每年每千人中的活产婴儿数。死亡率是每年每千人中的死亡人数。自然增长是两者之差。
Birth Rate = (live births ÷ total population) × 1000
Death Rate = (deaths ÷ total population) × 1000
Natural Increase = Birth Rate − Death Rate
If the result is positive, the population grows naturally; if negative, it declines (unless migration offsets it).
若结果为正，人口自然增长；若为负，人口自然减少（除非移民抵消）。
9. Population Change: The Full Equation | 人口变化：完整公式
When both natural change and migration are considered, the total population change is calculated by adding natural increase and net migration. Net migration = immigrants minus emigrants.
当同时考虑自然变化和迁移时，总人口变化由自然增长加净迁移得出。净迁移 = 迁入人口 − 迁出人口。
Population Change = (Births − Deaths) + (Immigrants − Emigrants)
- Review data carefully: figures may be given as totals or rates; convert to the same unit — 仔细审题：数据可能以总数或比率给出，需转换为相同单位
10. Climate Graphs: Interpreting Temperature and Rainfall | 气候图表：解读气温与降水量
A climate graph plots average monthly temperature (°C) as a line and total monthly precipitation (mm) as bars on the same chart. The shape of the graph reveals climate type: summer maxima, winter minima, seasonal rainfall patterns.
气候图表以折线表示月平均气温（°C），以柱状图表示月总降水量（mm），两者叠在同一张图上。图表的形状揭示气候类型：夏季最高温、冬季最低温、季节性降水模式。
- Temperature range = max monthly temperature − min monthly temperature — 气温年较差 = 最高月均温 − 最低月均温
- Total annual rainfall = sum of all monthly precipitation totals — 年总降水量 = 各月降水量之和
11. River Discharge: Measuring Flow | 河流流量：测量径流
River discharge is the volume of water passing a point in the river per second. It is measured in cubic metres per second (cumecs). Discharge increases downstream as more tributaries join, and rises during storms.
河流流量是每秒通过河流某一点的水量，以立方米每秒（cumecs）计量。流量通常向下游增加，因为更多的支流汇入，并在暴雨期间升高。
Discharge (Q) = cross‑sectional area (A) × velocity (V)
- Area = width × average depth; velocity can be timed using a float over a fixed distance — 面积 = 宽度 × 平均水深；流速可用浮标在固定距离内计时测量
12. Key Geographical Principles to Remember | 需要记住的关键地理定理
Beyond calculations, Year 7 geography introduces several core concepts that act as ‘rules of thumb’ when explaining patterns and processes:
除了计算，Year 7 地理还引入一些核心概念，如同解释规律和过程的“经验法则”：
- Contour lines close together indicate steep slopes; far apart indicate gentle slopes — 等高线密集表示陡坡，稀疏表示缓坡
- Settlement sites are often chosen for flat land, water supply, and shelter — 聚落选址常考虑平坦地形、水源和庇护
- Weather and climate are different: weather is short‑term conditions; climate is the long‑term average — 天气与气候不同：天气是短期状况，气候是长期平均
- Rivers erode, transport and deposit; erosion rates depend on energy and rock type — 河流会侵蚀、搬运和沉积；侵蚀速率取决于水能和岩石类型
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