angular resolution, lower aliasing effect, and consistent connectivity (Wang and Ai 2018). Annex 2 presents a detailed description of the methodology used to create the hexagon-level data set.

To measure nighttime light before the project, the latest year for which nightlights data are available before the project was appraised is used. To measure nightlights after the project is completed, the longest gestation period possible for WEBs to emerge is used, which runs until 2012.<sup>15</sup> The average sum of light (SOL) value for hexagons within 20 kilometers of the project’s alignment one year prior to project appraisal is 1,337. This value increased to 2,064 in 2012—the last year for which nightlights data are available.

## **3.5. Human Settlements**

We use the Global Human Settlement Layer (GHSL) (Pesaresi et al. 2016) to estimate built-up land cover and urban settlements within the analyzed hexagons. GHSL is based on the European Commission’s Global Human Settlement Grid. This data set utilizes a degree of urbanization model to determine to what degree an area is developed. The data are separated into high-density (cities or large urban areas), low-density (towns and suburbs), and rural grids. Each of these categories is represented by a numerical value ranging from 0 to 3. These numerical values are summed as total values for each year available in the data set. The sum of values represents per-hexagon degrees of urbanization.

# **4. Empirical Strategy**

In addition to understanding whether a large transport corridor investment can yield WEBs on average, it is important to understand the relationship between the realization of WEBs and the environment in which the project is being designed and implemented—that is, the local initial conditions and country characteristics—and the design characteristics of the project itself.

For example, the geographic scope of a project may have a significant impact on the realization of WEBs. On the one hand, projects with a larger expanse (national or transnational) may create a strategic connection with extra catalytic effects on the economy. On the other hand, the inherent difficulty in implementing such large and complex projects may significantly delay or even taper the ultimate impact on the economy. Similarly, as compared with projects on a flatter terrain, projects on more rugged terrains may preclude the local communities from benefiting from the strategic connectivity created by the project if suitable first and last mile connectivity is not provided. However, if the level of initial connectivity in more rugged terrains is lower, then the benefits from the development of a strategic transport corridor including secondary connectivity (roads) may be higher, compared with the same corridor being developed on a flatter terrain that already has a higher level of initial connectivity. Such questions should be assessed empirically to understand the key conditional relationships for successful project design.

The paper assesses whether transport corridors appear to spur higher economic activity around them, considering the following questions:

- Are the corridors initiated in countries that are richer, bigger, and easier to connect (initial conditions)?

> 15 Comparable nightlights data are available between 1992 and 2012 (inclusive), which limits the number of projects in the sample. Three of the projects were appraised in 1991. For these projects, nightlights data from 1991 were used. In addition, four projects closed in 2012. For these, 2012 data for nightlights were used.

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