![]() Many of the features shown on paper maps, including transportation routes, rivers, and political boundaries, can be represented effectively in digital form using the vector data model. The vector strategy is well suited to mapping entities with well-defined edges, such as highways or pipelines or property parcels. The vector data model is consistent with how surveyors measure locations at intervals as they traverse a property boundary. ![]() ![]() In this case, two polygons (filled with blue) represent the reservoir. A series of line segments that begin and end at the same node form polygon features. In this case, the line feature colored red represents the highway. Line segments connect nodes to form line features. The small squares are nodes: point locations specified by latitude and longitude coordinates. The graphic above right illustrates how the entities might be represented with vector data. The aerial photograph above left shows two entities, a reservoir and a highway. Requires the QuickTime plugin, which is available free at the Apple Quicktime download site. View the same animation in QuickTime format (vector.mov, 1.6 Mb) here. When the points are connected by lines or arcs, the sampled points form line features and polygon features that approximate the shapes of their real-world counterparts.Ĭlick the graphic above to download and view the animation file (vector.avi, 1.6 Mb) in a separate Microsoft Media Player window. The vector approach involves sampling either specific point locations, point intervals along the length of linear entities (like roads), or points surrounding the perimeter of areal entities (like water bodies such as lakes or oceans). Vector and raster data are, in essence, two distinct sampling strategies: vector and raster. And just as serious opinion polls are based on sound principles of statistical sampling, so, too, do geographic data represent reality by measuring carefully chosen samples of locations. In much the same way that public opinion is measured through polls, geographic data are constructed by measuring representative samples of locations. The Earth is too big, and the number of unique locations is mathematically infinite. No geographic data set represents every possible location, of course. Digital geographic data are encoded as alphanumeric symbols that represent locations and attributes of locations measured at or near Earth's surface. Recall that data consist of symbols that represent measurements. The two predominant data representation strategies are known as " vector" and " raster." Several different approaches to representing locations and extents in digital form were developed. ![]() One of the first challenges they faced was to convert the graphical data stored on paper maps into digital data that could be stored in, and processed by, digital computers. Thanks so much in advance! Sorry for my silly newbie question.Innovators in many fields, including engineers, computer scientists, geographers, and others, started developing digital mapping systems in the 1950s and 60s. Is this map raster or vector, and how can you tell in actual practice? It doesn't really seem anything like the examples from the lecture, where I saw the same road mapped in both vector or raster, or the same lake, for example. Here is where I am lost! I am looking at this interative map of where Thanksgiving dinner ingredients are produced, for example ( link), and it is a basic map of the united states with circles in each county, and the size of the circles represent how much of the ingredient is farmed in that county.Īttributes associated with each circle would be county name, # of acres of ingredient farmed there, and # of farms.īut for whatever reason, something is just not clicking for me to understand if this is raster or vector data - I want to guess raster because it seems like simpler data? but truly I have no idea. This all makes sense when thinking about very basic maps, but for an assignment this week I am supposed to take examples of maps and discuss weather the data presented is showing a vector or raster model of data. I have grasped that in theory, the difference between vector data and raster data is that vector data uses a series of lines and points to show where features are, where raster data is made up of pixels. Hello! I'm taking an online GIS course and we are covering spatial data models.
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