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: Vector graphics, on the other hand, are composed of paths instead of dots, and can be scaled without reducing the quality of the image.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. Therefore, bitmap images will appear blurry if they are enlarged. If you zoom into a bitmap image, regardless of the file format, it will look blocky because each dot will take up more than one pixel. Therefore, most images you see on the web are compressed bitmaps. Compressed bitmaps are significantly smaller than uncompressed BMP files and can be downloaded more quickly.

Each format uses a different type of compression, but they all represent an image as a grid of pixels. Other bitmap image formats, such as JPEG, GIF, and PNG, incorporate compression algorithms to reduce file size. This simple, universal image format can be recognized on nearly all platforms, but is not very efficient, especially for large images. It includes a header, which defines the size of the image and the number of colors the image may contain, and a list of pixels with their corresponding colors. The standard, uncompressed bitmap format is also known as the ' BMP' format or the device independent bitmap (DIB) format. There are several different bitmap file formats.

Together, these dots can be used to represent any type of rectangular picture. In a standard bitmap image, each dot can be assigned a different color. When viewed at 100%, each dot corresponds to an individual pixel on a display. A bitmap (or raster graphic) is a digital image composed of a matrix of dots.

Raster graphics definition