Thematic maps can also result from geoprocessing operations that combine data from various sources, such as vector, raster, and terrain data. This groups the values of multispectral data into classes (such as vegetation type) and assigns a categorical value. A common analysis application is classifying a satellite image into land-cover categories. Rasters representing thematic data can be derived from analyzing other data. The raster in the image below displays elevation-using green to show lower elevation and red, pink, and white cells to show higher elevation. Elevation values measured from the earth's surface are a common application of surface maps, but other values, such as rainfall, temperature, salinity, magnetic properties, and density of materials can also define surfaces that can be spatially analyzed. They also provide a regularly spaced representation of surfaces. They provide a method of storing the continuity as a surface. Rasters are well suited for representing data that changes continuously across a landscape (surface). The following image is used as a basemap for road data. The main sources of raster basemaps are orthorectified images from aerial, drone, and satellite imagery, and scanned maps. For example, orthoimages that are displayed under other GIS layers allow map users to confirm that map layers are spatially aligned and represent real objects, as well as provide additional contextual information. In a GIS, image and raster data is typically used for the following:Ī common use of image data in a GIS is as an image background for other feature layers. Image and raster data is useful for a wide range of applications. They can be displayed with geographic data and are used to convey additional information about map features. Thematic and digital pictures are often used as attributes in tables. Pictures can include scanned maps or drawings and building photographs.Ĭontinuous images can be displayed as data layers along with other geographic data on a map but are often used as the source data for image analysis.Thematic data (also known as discrete data) represents features such as land use and soils data.Continuous data represents spectral data, such as satellite, aerial, and drone images, and physical and environmental data such as elevation and temperature.Rasters are digital images collected by aircraft, drones, satellites, ground and water-based sensors, digital pictures, and scanned maps.ĭata stored in a raster format represents real-world phenomena in the following ways: In its simplest form, a raster consists of a matrix of pixels (or cells) organized into rows and columns (or a grid) in which each pixel contains a value representing information, such as image reflectance or temperature.
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