We have said spatial data relate to conditions, facts, and objects in three-dimensional space. Most spatial data that now exist use a two-dimensional referencing scheme such as latitude/longitude (or projections thereof) or street addresses. Unless the dataset is specifically one that considers the matter of altitude, this third coordinate is either included as part of the attribute data (rather than part of the locational identifier) or is implied by the nature of the data. For example, if the data describe soil characteristics, one understands that the top few feet of the Earth’s crust, regardless of altitude, are being described.
Data types that might be part of spatial datasets are exemplified in Table 2-1.
|Soils||Types, physical and chemical properties|
|Vegetation||Species composition, age|
|Wildlife habitat||Types, carrying capacity|
|Hydrology||Ground and surface water, volume, flows|
|Geology||Rock types, minerals and ores, physical and chemical properties, oil and gas deposits|
|Physiography||Elevation, slope, aspect|
|Land use||Activity types, structure types, zoning|
|Land cover||Types, facts about what covers the surface|
|Transportation facilities||Types, capacity, schedules, condition, age|
|Utility distribution systems||Service areas, capacity, historical features and landmarks—importance, condition, ownership, use|
|Census districts||Population, housing, other demographic information ...|