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intro/ci_explained.md

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 # Critical Infrastructure Explained
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+Critical Infrastructure (CI) refers to the essential services and assets that form the backbone of a functioning society and economy. These infrastructure systems are vital for public health, safety, and economic well-being, supporting various activities ranging from transportation to energy distribution. CI systems are susceptible to a wide range of threats, both natural and human-made, including natural disasters, terrorism, and poor maintenance. We categorize critical infrastructure (CI) network into seven overarching systems: transportation, energy, water, waste, telecommunication, education, and health. This classification aligns with widely accepted frameworks in the literature (Hallegatte et al., 2019; Hall et al., 2019; Thacker et al., 2019; United Nations Office for Disaster Risk Reduction, 2015), and highlights the growing recognition of the importance of educational and health-related infrastructure (United Nations Office for Disaster Risk Reduction, 2015). 
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+Each of these seven CI systems is further subdivided into ten subsystems, with each subsystem containing two or more specific types of infrastructure. For example, the telecommunication subsystem encompasses communication towers and masts. To represent the global landscape of CI, a total of 81 OpenStreetMap (OSM) tags were selected to identify 39 different infrastructure types (Popescu & Simion, 2011). This breakdown of critical infrastructure types enables a more granular approach to risk and damage assessments by providing detailed categorizations and geospatial data on the global infrastructure network.
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+![Distribution and statistics of unique CI assets extracted from OSM](https://media.springernature.com/full/springer-static/image/art%3A10.1038%2Fs41597-022-01218-4/MediaObjects/41597_2022_1218_Fig3_HTML.png?as=webp)
+*Figure 1: Distribution and statistics of unique CI assets extracted from OSM (Nirandjan et al., 2022).*
+
+The spatial distribution of critical infrastructure assets varies across countries and income levels. **Figure 1** illustrates this distribution across space and provides statistics for unique CI assets extracted from OpenStreetMap (OSM). Panel (a) shows the number of unique CI assets per country, revealing that the highest number of unique assets is found in high-income countries such as the United States, Germany, and Japan, while the lowest number is observed in Small Island Developing States (SIDS) and other small islands. Panel (b) breaks down the percentage of unique CI assets according to four income classes, categorized by the seven main CI systems. It shows that high-income countries account for 60.8% of the extracted OSM elements, while low-income countries contribute only 3.3%. Panel (c) illustrates the dominant role of the transportation system in the extracted CI elements, accounting for 84% of all unique assets. This dominance is largely due to the vast number of roads, particularly tertiary roads, which make up the bulk of the transportation infrastructure.
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+More specifically, we categorize CI into the following types and subtypes:
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+1. **Transportation**  
+   The transportation system includes three subsystems: roads, railways, and airports. Roadways are further categorized into primary, secondary, and tertiary roads, with tertiary roads making up the majority of assets. The system facilitates the movement of people, goods, and services, and its disruption can cause widespread economic and societal impacts. Critical infrastructure types include:
+   - Roads (primary, secondary, tertiary)
+   - Railways
+   - Airports
+
+2. **Energy**  
+   The energy infrastructure is crucial for the generation, transmission, and distribution of electricity. The seven key types selected for energy representation include cables, power lines (major and minor), substations, and power plants. Disruptions to this system can result in significant economic losses and widespread outages. Key elements include:
+   - Power cables
+   - Power lines
+   - Minor power lines
+   - Power towers
+   - Power poles
+   - Power plants
+   - Substations
+
+3. **Telecommunication**  
+   Telecommunication networks enable communication through telephone, radio, and internet systems. This system includes communication towers and masts. Towers are generally taller and support multiple applications, while masts are used for single applications. Key infrastructure types include:
+   - Communication towers
+   - Masts
+
+4. **Water**  
+   The water system provides the infrastructure needed to supply clean and potable water. The five selected infrastructure types are critical for the extraction, distribution, and storage of both potable and non-potable water. Critical components include:
+   - Water towers
+   - Water wells
+   - Covered reservoirs
+   - Reservoirs
+   - Water works
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+5. **Waste Management**  
+   The waste management system is divided into two subsystems: solid waste and water waste. The solid waste subsystem consists of transfer stations and landfills, while the water waste subsystem includes water treatment plants. This system ensures proper disposal and treatment of waste materials. Key infrastructure includes:
+   - Waste transfer stations
+   - Landfills
+   - Water waste treatment plants
+
+6. **Health**  
+   Health infrastructure supports public health and medical services, ensuring the availability of hospitals, clinics, and pharmacies. A variety of facilities are considered under this system, ranging from general medical services to specialized centers. Examples include:
+   - Hospitals
+   - Clinics
+   - Pharmacies
+   - Doctors
+   - Laboratories
+   - Birthing centers
+   - Rehabilitation centers
+
+7. **Education**  
+   Educational infrastructure ensures the availability of facilities for learning and knowledge dissemination. The five infrastructure types in this system include:
+   - Schools
+   - Universities
+   - Colleges
+   - Kindergartens
+   - Libraries
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+As part of our damage and risk assessments, understanding these infrastructure types and their vulnerabilities is crucial. In the sections that follow, we will explore how each CI system can be assessed for risks and damages caused by natural or human-made threats.

intro/exposure.md

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 # Exposure
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+Exposure refers to the presence of people, assets, or critical infrastructure (CI) systems in areas that are susceptible to natural hazards, such as floods, earthquakes, storms, or other disasters. When CI systems are exposed to these hazards, their functionality can be compromised, leading to cascading effects across dependent sectors. For example, damage to energy infrastructure during a storm can disrupt health services, transportation, and communication networks.
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+In risk assessments, exposure is a key component as it quantifies the physical presence of infrastructure within hazard-prone areas. Without understanding which infrastructure systems are exposed and where, it is impossible to accurately assess potential risks. This is where geospatial data, such as that provided by OpenStreetMap (OSM), becomes essential for mapping exposure and conducting vulnerability assessments.
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+Central to our assessment is the integration of open data collected and provided by OpenStreetMap. The goal of this platform is to create and distribute free and openly accessible geospatial and attributional information on the world’s features. With 4.5 million map changes/day, the OSM database counts approximately 15.5 billion georeferenced features as of 26th November 2020. The integration and pre-processing of OSM data provide a detailed, high-resolution understanding of infrastructure exposure on a global scale. The use of OSM allows for a standardized approach to assessing the vulnerability of CI systems by identifying key assets and their proximity to known hazard zones. 
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+Geographical features in OSM are projected in the form of nodes, ways, and relations. A node represents a specific point in space and is defined by its latitude and longitude (e.g., telecommunication tower). The datatype "ways" exists as a line segment that is connected by two or more nodes (e.g., road). A polygon (or area) is described as a closed way, created when the last node of a series of line segments is connected to the beginning (e.g., hospital). Another datatype, "relations", is an ordered list of features that groups nodes, ways, and relations into a larger unit. 
+An example of unprocessed OSM data, including a breakdown of the basic datatypes, is shown in **Figure 2**. Each georeferenced element in OSM has an ID number that uniquely identifies it, along with details such as the user who modified the element and the time of last modification. Elements can be further specified by a list of attribute tags in the form of key-value pairs, whereby the value provides more detail to the key identifier. For example, primary roads that often link larger towns are specified under the key ‘highway’ in combination with the value ‘primary’.
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+![OSM Data Types](https://media.springernature.com/full/springer-static/image/art%3A10.1038%2Fs41597-022-01218-4/MediaObjects/41597_2022_1218_Fig2_HTML.png?as=webp)
+*Figure 2: Visualization of raw OpenStreetMap data of a given area, with a breakdown by the datatypes (Nirandjan et al., 2022).*
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+