📚 OCR A Level Year 13 Geography: Formula & Theorem Quick Reference Handbook | OCR A Level Year 13 地理：公式定理速查手册
Welcome to this quick reference handbook designed for Year 13 students following the OCR A Level Geography specification. It brings together the essential quantitative formulas, statistical tests and key geographical theorems you need to apply in your NEA, fieldwork analysis and exam questions. Each entry is presented with a clear explanation, the mathematical expression and the context in which it is used. Use it as a revision checklist to ensure you can select and calculate the right measure for any given data set.
欢迎使用这本为 OCR A Level 地理 Year 13 学生打造的公式定理速查手册。它汇总了独立调查分析、实地考察和考试题目中必需的定量公式、统计检验与关键地理定理。每个条目都配有清晰的解释、数学表达式以及使用情境。请把它当作复习清单，确保你能够为任何给定数据选择并计算出正确的度量指标。
1. Population Change Formulas | 人口变动公式
Natural increase rate (often called natural population change) is the simplest measure of population growth ignoring migration. It is calculated by subtracting the crude death rate from the crude birth rate. Both rates are usually expressed per 1000 people per year.
自然增长率（常称人口自然变动）是忽略迁移的最简单的人口增长度量。它由粗出生率减去粗死亡率得出。两个比率通常都以每千人每年为单位表示。
Natural Increase = CBR – CDR (per 1000)
When net migration is included, the overall population growth rate (as a percentage) combines the difference between births and deaths with the net migration rate. A common conversion from per‑1000 values to a percentage divides the sum by 10.
当纳入净迁移时，总人口增长率（百分比）将出生‑死亡差值与净迁移率结合。常用的千分比转换为百分比的方法是将总和除以 10。
r (%) = (CBR – CDR + NMR) / 10
The ‘rule of 70’ provides a quick estimate of the doubling time of a population. It assumes a constant exponential growth rate and is widely used in demographic transition analysis.
“70 法则”可快速估算人口翻倍时间。它假设恒定的指数增长率，广泛应用于人口转变分析。
Doubling Time (years) = 70 / r (r in %)
Net migration rate itself is computed as the difference between immigrants and emigrants in a year, divided by the mid‑year population, then multiplied by 1000. This appears frequently in topics covering migration patterns and settlement change.
净迁移率本身由一年内迁入与迁出的人口差额除以年中人口再乘以 1000 得出。在涉及迁移模式与聚落变化的主题中频繁出现。
NMR = (I – E) / P × 1000
2. Rank‑Size Rule (Zipf’s Law) | 位序‑规模法则（齐普夫定律）
The rank‑size rule describes the idealised urban hierarchy in a country where the population of the nth largest city is inversely proportional to its rank. It is a key concept when studying settlement systems and urban growth.
位序‑规模法则描述了理想化的城市等级体系，其中第 n 大城市的人口与其位序成反比。它是研究聚落体系与城市增长的核心概念。
Pₙ = P₁ / n
Deviations from this rule often indicate a primate city distribution, where one city dominates the urban system. You may be asked to plot city‑rank data on logarithmic scales to test the rule’s validity.
偏离该法则通常表明存在首位城市分布，即一个城市主导整个城镇体系。考试可能要求你将城市位序数据绘制在对数坐标上以检验其有效性。
3. Location Quotient (LQ) | 区位商（LQ）
The location quotient is an index of economic specialisation. It compares the concentration of a particular industry in a region with the concentration of the same industry at the national level. An LQ greater than 1 means the region is specialised in that activity.
区位商是衡量经济专业化的指标。它比较某区域内特定产业的集中度与全国同一产业的集中度。LQ 大于 1 表示该地区在该产业上具有专业化优势。
LQ = (e / E) ÷ (n / N)
Here e is regional employment in the chosen industry, E is total regional employment; n is national employment in that industry, and N is total national employment. This tool is regularly used in regeneration and economic change essays.
其中 e 为区域所选产业的就业人数，E 为区域总就业；n 为全国该产业就业人数，N 为全国总就业。该工具常用于再生与经济变迁论文中。
4. Gini Coefficient and Lorenz Curve
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