There are a few key formats used for cartography on a regular basis as both input and output formats discussed here, including PNG, JPEG, TIFF, and GIF. Raster data can be distributed in a format as simple as a text file or in more sensor specific binary formats (see the Raster Data Model). There are numerous raster formats and specifications that leverage raster data. The choice of bit-depth for elevation data is dependent on the accuracy and range of the data. Elevation data is commonly distributed as 16-bit or 32-bit integer or floating-point raster images with the full value range available per pixel designating an elevation value in the specified unit. Some data formats are single band with the bit depth, or the number of bits storable for a given data type, allocated to each pixel in that band. A 32-bit RGB image adds an extra alpha channel that allows for varying transparency in the image (Porter and Duff, 1984). For instance, a 24-bit RGB image has 8-bits each for red, green, and blue channels (see Color Theory). In many formats, the bit depth designates the richness of color and the image can be thought of as being constructed of color bands where each band represents a color channel of the color raster. Each pixel has a specified number of bits (binary digit) that designate the information that can be stored per pixel. Raster datasets are an array of pixels typically in a rectangular grid (Wise, 2000). Raster formats share the fundamental building block of a pixel (picture elements), the smallest unit of a raster dataset. This entry covers the primary raster formats applicable to cartography, considerations when using them as well as raster source types that are used for map production. When producing raster output, the device target, such as print, screen display, and the map content, should be considered when making a choice of raster format to use. When designing and producing maps, the quality, resolution, and color characteristics of raster sources should be considered. In many cases, a map product may be a combination of raster and vector sources. See Vector Formats & Sources for more information. Raster formats use pixels at a known resolution to convey information, whereas vector formats use geometric primitives that are generally resolution independent. vector: datasets defined as geometric primitives rather than raster dataĬartographers use raster and vector data sources to produce maps (Kimerling et al., 2009) and deliver maps in raster or vector formats.resolution: the number of distinct pixels that can be displayed in a measured space.raster: datasets defined as an array of pixels.pixel: a portmanteau of ‘picture element’, the smallest unit of a raster.lossy: compression that results in data loss.lossless: compression that does not result in the loss of data.LIDAR: Light Detection and Ranging, a technology for collecting data using laser reflectance.gamut: a subset of colors in a color model representable in a color space. dithering: a technique for minimizing content loss during reduction of color depth by inserting pixel noise. color space: a definition of colors in a color model which allows for repeatable reproduction of color.color model: a mathematical model for representing colors such as RGB or CMYK.bit depth: the number of bits storable for a given data type.bit: a portmanteau of binary digit, the smallest unit of storable information.bands: a defined channel or subset of a raster dataset, for instance, the red channel of an RGB image.
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