老板油烟机型号8010:GIS专业英语翻译

Representing Maps as Numbers(3.1)
.GIS requires that both data and maps be represented as numbers.
.The GIS places data into the computer's memory in a physical data structure,i.e.files and directories.
.Files can be written in binary or as ASCII text.
.Binary is faster to read and smaller,ASCII can be read by humans and edited but uses more space.
.Programmers use hexadecimal as shorthand for binary,since two hexadecimal digits correspond to 8 bits(a byte).
.A logical data model is how data are organized for use by the GIS.
.GISs have traditionally used the logical data models of either raster or vector,and for attributes the flat file.
.A raster data model uses a grid.
-One grid cell is one unit or holds one attribute.
-Every cell has a value,even if it is "missing."
-A cell can hold a number or an index value standing for an attribute.

Sec.3.7 Study Guide
-A cell has a resolution,given as the cell size in ground units.
-Points and lines in raster format have to move to a cell center.
-Lines can become fat.Areas may need separately coded edges.
-Each cell can only be owned by one feature.
-As data,all cells must be able to hold t maximum cell vaule.
.Raster are easy to understand,easy to read and write,and easy to draw on the screen.
.A vector data model uses points stored by their real coordinates.
-lines and areas are built fro sequences of points in order.
-lines have a direction to the ordering of the points.
-Polygons can be built from points or lines.
-Vectors can store information about topology.
-Have to use TIN to represent volumes.
.Vector can represent point,line and area features very accurately.
.Vectors are far more efficient than grids.
.Vectors work well with pen and light plotting devices,and tablet digitizers.
.Vectors are not good at continuous coverages or plotters that fill areas.
.Vectors are like the music of Beethoven,rasters are like Mozart's.

Structuring Attributes(3.2)
.Attribute data are stored logically in flat files.
.A flat files is a matrix of numbers and values stored in rows and columns,like a spreadsheet.
.Both logical and physical data models have evolved over time.
DBMSs use many different methods to store and manage flat files in physical files.

Structuring Maps(3.3)
.A GIS map is a scaled down digital representation of point,line,area,and volume features.
.While most GIS systems can handle raster and vector,only one is used for the internal organization of spatial data.
.VECTOR
.At first,GISs used vector data and cartographic spaghetti structures.
.Vector data evolved the Arc/Node model in the 1960s.
.In the Arc/Node model,and area consist of lines and a line consists of points.
.Points,lines,and areas can each be stored in their own files,with links between them.
.The topological vector model uses the line(arc) as a basic unit.Areas(polygons) are built up from arcs.