A location's irreplaceability refers to the degree of difficulty with which it can be replaced by other locations. For example, the irreplaceability of airports, hospitals, and ATMs varies, and that between hospitals is also different. They differ in both the number of users and the extent of service area. Quantifying the location's irreplaceability provides guidance for urban planning, such as siting of public resources. Existing methods for quantifying an urban location's irreplaceability do not consider human activity at the location, therefore the revealed irreplaceability may deviate from the resident's perceptions. To address this issue, we use origin-destination flows to reflect human activity. We propose a flow-based locational measure, I-index, to quantify the location's irreplaceability. It can be viewed as ‘H-index of flow’ where we regard locations as scientists, flows as papers. I-index of a location is the maximum value of i such that at least i flows with a length of at least α ∗ i meters have reached this location, where α is the conversion factor that can be determined adaptively from the flow dataset. I-index elegantly combines the flow volume and length into a single value. The effectiveness of the I-index is validated by simulation experiments. Two case studies show that the hospital's irreplaceability strongly correlates with the hospital bypass behavior and locations with strongly mixed urban functions are more irreplaceable. The implications for urban planning are further discussed.

一个地点的不可替代性是指它可以被其他地点取代的难易程度。比如机场、医院、ATM的不可替代性各不相同，医院之间的不可替代性也不同。它们在用户数量和服务区域范围上都不同。量化位置的不可替代性可为城市规划提供指导，例如公共资源的选址。现有的量化城市位置不可替代性的方法没有考虑该位置的人类活动，因此揭示的不可替代性可能会偏离居民的感知。为了解决这个问题，我们使用起点-终点流来反映人类活动。我们提出了一个基于流量的位置度量，I-index，来量化位置的不可替代性。它可以被视为“流量的 H 指数”，我们将地点视为科学家，将流量视为论文。一个位置的 I-index 是i这样至少i个长度至少为α  *  i米的流已经到达该位置，其中α是可以从流量数据集自适应确定的转换因子。I-index 优雅地将流量和长度组合成一个值。I-index 的有效性通过模拟实验得到验证。两个案例研究表明，医院的不可替代性与医院绕行行为密切相关，城市功能强烈混合的地点更不可替代。进一步讨论了对城市规划的影响。