I-index

This repository contains a Python implementation of the I-index, a novel flow-based locational measure to quantify an urban location's irreplaceability.

Wang, X., Chen, J., Pei, T.*, Song, C., Liu, Y., Shu, H., … Chen, X. (2021). I-index for quantifying an urban location’s irreplaceability. Computers, Environment and Urban Systems, 90, Article 101711. https://doi.org/10.1016/j.compenvurbsys.2021.101711

Brief Introduction of the I-index

Following the philosophy of the well-known H-index in bibliometric analysis, which quantifies a scientist's academic achievements by both number and citations of papers, the I-index elegantly combines the flow volume and flow length into a single value. Formally, 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. The larger value of the I-index, the more flows are attracted and the longer these flows are, reflecting its irreplaceability or centrality. Figure below illustrates an example of the calculation of the I-index and its geometric interpretation assuming α = 1.

Usage

Flow_I_index.py contains the calcuation of the I-index given an OD flow dataset (bj_od_sample.csv) and a grid file (grid.csv)

Inputfile:

bj_od_sample.csv

• odid (int)：OD flow ID
• olon (float)：longitude of O point (WGS84)
• olat (float)：latitude of O point (WGS84)
• dlon (float)：longitude of D point (WGS84)
• dlat (float)：latitude of D point (WGS84)

grid.csv

• polyid (int)：polygon ID
• geometry (str)：wkt of the polygon (WGS84)

Outputfile:

grid_iidx.csv

• polyid (int)：polygon ID
• alpha (float)：conversion factor
• I_index (float)：I-index
• flowtotalcnt (float)：total flow volume
• flowtotallength (float)：total flow length (unit:km)

Citation

If you use this code in your research, please cite our paper:

@article{WANG2021101711,
title = {I-index for quantifying an urban location's irreplaceability},
journal = {Computers, Environment and Urban Systems},
volume = {90},
pages = {101711},
year = {2021},
issn = {0198-9715},
doi = {https://doi.org/10.1016/j.compenvurbsys.2021.101711},
url = {https://www.sciencedirect.com/science/article/pii/S0198971521001186},
author = {Xi Wang and Jie Chen and Tao Pei and Ci Song and Yaxi Liu and Hua Shu and Sihui Guo and Xiao Chen},
keywords = {Locational measure, Irreplaceability, Origin-destination flow, Flow mapping, H-index}
}