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Raster vs. Vector Explained

Raster Images vs. Vector Images

The terms raster and vector are used throughout any discussion involving surveying and mapping. They both refer to specific types of data. Raster data is organized as a matrix or grid that has rows and columns; each row/column intersection is a cell or pixel. Each cell has a value, for example, an elevation. Images and digital elevation models are rasters. They are a specific number of pixels high and wide, with each pixel representing a certain size on the ground; for example, Landsat satellite images are 185×185 km in size. Each

pixel is 30 ×30 m in size.

Vector data is represented as coordinates that define points or points that are strung
together to make lines and polygons. This data often has an associated table of infor-
mation, one for every feature (point, line, or polygon) in the dataset. Keeping these dis-
tinctions in mind will help you better understand the remaining parts of this chapter.


Raster Images

Raster images are also called Bitmap images, pixels are also called dots, and dots-per-inch (dpi) sometimes called pixels-per-inch (ppi) although technically they have distinct meaning I may use those terms interchangeably in surveying discussions.

Raster images' dimensions are measured in pixels. Because raster images cannot be enlarged without losing quality, different suppliers have specific size requirements for their processes; they require a specific pixel resolution: a specific amount of pixels within each inch. The amount of pixels within each inch in the image represents the image pixel resolution or ppi (pixels per inch).


Vector Images

Vector graphics are made of mathematical calculations that form objects or lines - they do not use pixels therefore are resolution-independent which means they can be used at the highest resolution the output device allows:

Vector graphics can be enlarged and printed at ANY SIZE!
Instead of pixels, vector graphics use objects and lines (shapes) to represent images. Vector files can be scaled to any size without losing quality.

Some Vector programs have two different views; preview/normal view which displays the image as we normally would see it and an outline/wireframe view which displays the outline of every object in the file. This vector outline/wireframe is important to some companies like engraving & vinyl-cut signs because it guides the equipment they use to create their products.

Just thought i would share this, as it confuses surveyors at times.  Not all of the time, but sometimes.

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