The key point is that all of this data is represented as a grid of (usually square) cells. In GIS, the pixel values may represent elevation above sea level, or chemical concentrations, or rainfall etc.
Simplifying slightly, a digital photograph is an example of a raster dataset where each pixel value corresponds to a particular colour. Raster data is made up of pixels (or cells), and each pixel has an associated value. However, the distinction between vector and raster data types is not unique to GIS: here is an example from the graphic design world which might be clearer. In GIS, vector and raster are two different ways of representing spatial data. Latitudes and Longitudes in Raster data are displayed in the form of closed shapes where each pixel has a particular latitude and longitude associated with it. Latitudes and Longitudes in Vector data are displayed in the form of lines, points, etc.
The difference is in the way they are displayed. Raster models are useful for storing data that varies continuously, as in an aerial photograph, a satellite image, a surface of chemical concentrations, or an elevation surface.Īll I have understood from the above is that both vector and raster data constitute of "latitudes and longitudes", only. Raster data model: A representation of the world as a surface divided into a regular grid of cells. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets. After the header, the string of data for each cell appears, starting in the upper left corner of the grid, with each value separated by a space (space delimited) and each row separated by a carriage return.įor more information on GRID ASCII files, please go to the ESRI website.ĮSRI ® and ARC/INFO ® are registered trademarks of the Environmental Systems Research Institute, Inc.ĮNVI ® is a registered trademark of Better Solutions Consulting LLC.Vector data model: A representation of the world using points, lines, and polygons. The next header line provides the cell (pixel) size, and the optional sixth line is for the missing value code. Some files present "xllcenter" instead of corner - this is an acceptable format as well. In the example file fragment above, the first two header lines describe the number of columns and rows in the file, and the next lines provide the coordinates for the raster that represents the lower left corner of the data set. The first 5 lines should appear automatically when the file is generated from ARC/INFO ®, but if you are having trouble importing files, this may be the source of the problem. To import GRID ASCII files, the file must begin with a header - the first 5 lines in the header are required, while the sixth (listing a value assigned to missing data) is optional. GRID files contain only one variable, although you may import several GRID files with the same spatial coordinates: choose a custom import. The GRID format is a proprietary ESRI ® format for raster data. BoundarySeer can import these files directly. Importing digital elevation model files (*.dem)ĭEM files are USGS digital elevation model files that contain georeferencing information. These files are imported directly into BoundarySeer unless the file contains insufficient georeferencing information. GeoTIFF and DRG files are, essentially, georeferenced TIFF files. Importing georeferenced image files (GeoTIFF and DRG files) BMP files cannot currently be imported into BoundarySeer, but that capability is expected soon. These files contain no georeferencing information, and so they must be georeferenced on import or by using the georeferencing dialogs found from the "Data" menu. TIFF and JPEG image files can be imported into BoundarySeer as rasters. Importing image file formats (TIFF, JPEG, BMP) BoundarySeer can import any of these files directly, as it reads in the georeferencing information in the header. Importing ENVI ® files (BIL, BIP, and BSQ)ĮNVI ® rasters can be saved in one of three different file formats, band sequential (BSQ), band interleaved by line (BIL) and band interleaved by pixel (BIP). BoundarySeer can import a number of raster data types, including ENVI ® files (BIL, BIP, and BSQ), image files (TIFF, JPEG, BMP), georeferenced images (GeoTiff and DRG), digital elevation models (DEM), and GRID ASCII. You can choose to import additional raster data sets at any time by choosing "Data" from the main menu, and then choosing "Import", and then "Raster". The import data option appears whenever you open a new project. Import formats for raster data Import formats for raster data
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