Raster format in gis11/23/2023 A raster model with pixels representing 10×10 meters (or 100 square meters) in the real world has a spatial resolution of 10 meters. Specifically, resolution is determined by measuring one side of the square pixel. The area covered by each pixel determines the spatial resolution of the raster model from which it is derived. Therefore, the more area covered per pixel, the less accurate the associated data values. The raster model will average all values within a given pixel to yield a single value. The advance of computer technology has made this second methodology increasingly feasible as computer storage issues no longer constrain large datasets as they were previously. Alternatively, the raster graphic can reference a database management system wherein open-ended attribute tables can be used to associate multiple data values to each pixel. The data type for that cell value can be either integer or floating-point. Each cell in a raster carries a single value, which represents the characteristic of the spatial phenomenon at a location denoted by its row and column. Typically, a single data value will be assigned to each grid locale. These squares are typically reformed into rectangles of various dimensions if the data model is transformed from one projection to another (e.g., from State Plane coordinates to UTM coordinates).īecause of the reliance on a uniform series of square pixels, the raster data model is referred to as a grid-based system. Accordingly, the vast majority of available raster GIS data are built on the square pixel. Although pixels may be triangles, hexagons, or even octagons, square pixels represent the simplest geometric form with which to work. These pixels are used as building blocks for creating points, lines, areas, networks, and surfaces. The raster data model consists of rows and columns of equally sized pixels interconnected to form a planar surface. If you are as generous as the author, you may indeed think of your raster dataset creations as sublime works of art. The neo-impressionist artist, Georges Seurat, developed a painting technique referred to as “pointillism” in the 1880s, which similarly relies on the amassing of small, monochromatic “dots” of ink that combine to form a larger image. Notably, the foundation of this technology predates computers and digital cameras by nearly a century. Each of these uniquely colored pixels, when viewed as a whole, combines to form a coherent image.įurthermore, all liquid crystal display (LCD) computer monitors are based on raster technology as they are composed of a set number of rows and columns of pixels. If you zoom deeply into the image, you will notice that it is composed of an array of tiny square pixels (or picture elements). Take a moment to view your favorite digital image. The ubiquitous JPEG, BMP, and TIFF file formats (among others) are based on the raster data model. Most likely, you are already very familiar with this data model if you have any experience with digital photographs. The raster data model is widely used in applications ranging far beyond geographic information systems (GIS).
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