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Global Resources lFigure 2. Relationships between density and distance are best illustrated by market access across geographic scales, an indicator of the economic opportunity of a location that measures the size of potential markets in its vicinity and the ease of reaching them. with almost six out of every 10 children stunted (i.e., too short for their age). To test how food security and under-nutrition relate to health services, researchers used georeferenced data and a “distance-decay” approach, which mea- sures the relationship between observed interaction patterns and distance when all other determinants of interaction are constant. To do this, researchers modeled Yemenis’ physical access to health-service provision in rural and urban areas by measuring the accessibility between population location (cluster of villages) and service facilities. Using high-resolution maps of georeferenced infra- structure (road networks, and urban and rural health facilities), topography (digital elevation models) and populated village locations, researchers were able to use travel time as a proxy for distance to more-accurately reflect the accessibility of health centers and hospitals to specific clusters of villages. An index for physical accessibility to healthcare-service provision then was computed by deriving the exponential distance-decay function related to household income and population. Creating an SDI IFPRI researchers used GIS technology to create a food-security Geodatabase model in Yemen that was ultimately used to create a Food Security Atlas. The 28 GEO W ORLD / JUL Y 2O11 specific aim of this holistic Geodatabase model was to increase the efficiency and effectiveness of infor- mation management and improve the decision-making abilities of governmental institutions in Yemen. Figure 3 shows the conceptual data model that incor- porates relevant variables to food security from the main sectors of Yemen’s economy. The food-security data model has five key components: 1. Physical and human geography 2. Food security and nutrition 3. Trade and infrastructure 4. Agriculture and water 5. Health The food-security data model design was established in compliance with the ISO 19110 international standard for geographic information methodology for feature cata- loging. Using Esri Geodatabase modeling techniques, IFPRI implemented the feature-cataloging concepts based on the fundamental principle of abstraction. Figure 4 summarizes the standard procedures and steps for designing and building the food-security geodatabase model. It includes the conceptual model composed of four basic activities: 1. Conceptual framework and guidelines 2. User needs assessment 3. Checking existing data models 4. Data inventory