text: In order to assess the disaster risk of an area, data on the following categories are required: Natural hazard Vulnerability + Elements at risk 4.1 Natural hazard Techniques for the assessment of natural hazards are reasonably adequate, but in some areas and in some scientific disciplines there may be deficiencies of basic data both in quantity and quality. For the natural phenomena of main interest - meteorological and hydrological phenomena, earthquakes and volcanoes - it is essential that data requirements for the assessment of natural hazard should be formulated and, where gaps are identified, urgent steps should be taken to close them. These steps are important since natural phenomena are complex, and for their complete description and future development a number of different parameters are required (thus a tropical cyclone is described in terms of its direction, speed of movement, maximum wind strength, the value of the surface pressure at its centre, etc..). The preparation of hazard maps presents no particular problems, given adequate data of reasonable quality. In order to establish risk, a planner would expect to be provided with hazard maps for each phenomenon which is known to occur in the area under consideration. For example, hazard maps might be prepared for the extent of flooding for one or more average return periods, for flooding due to river flows exceeding the bankfull discharge, and for flooding due to storm surges in coastal and estuarine areas, There might, in addition, be other hazards of a geological nature which would have to be mapped (for example fault lines, loose unconsoli- dated soils, etc) and overlaid. 4.2 Vulnerability Information on vulnerability is less plentiful, less reliable and less clearly defined than the information usually available on natural hazards themselves. Various categories of data are required, relating not only to the details of possible material damage, but also to the degree of 
analysis: The text discusses the assessment of disaster risk, which is closely related to the field of natural resources and environment. The text specifically focuses on natural hazards, vulnerability, and elements at risk, indicating that the category is more concerned with the physical environment and natural phenomena rather than human activities or social issues. The language used is technical and scientific, suggesting that the category is more related to science and technology.