Manoj Blog Spot Information (MBSI) is a blog where i will share my view in GIS and also i will discuss the problem posted by user.
Here i am starting the basic terms of GIS. First i am describing here the Topology
When asked if topology is a key concept of GIS, most GIS users will nod their heads in agreement. But ask these same folks about how topology is handled in shapefiles and the nodding heads give way to shrugging shoulders. Why should GIS users care about topology? What are the advantages and disadvantages of storing polygon data in shapefiles rather than coverages?
What Is Topology?
In 1736, the mathematician Leonhard Euler published a paper that arguably started the branch of mathematics known as topology. The problem that led to Euler's work in this area, known as "The Seven Bridges of Königsberg," is described in the accompanying article "Conundrum Inspires Topology." More recently, the United States Census Bureau, while preparing for the 1970 census, pioneered the application of mathematical topology to maps to reduce the errors in tabulating massive amounts of census data. Today, topology in GIS is generally defined as the spatial relationships between adjacent or neighboring features.
Mathematical topology assumes that geographic features occur on a two-dimensional plane. Through planar enforcement, spatial features can be represented through nodes (0-dimensional cells); edges, sometimes called arcs (one-dimensional cells); or polygons (two-dimensional cells). Because features can exist only on a plane, lines that cross are broken into separate lines that terminate at nodes representing intersections rather than simple vertices.
In GIS, topology is implemented through data structure. An ArcInfo coverage is a familiar topological data structure. A coverage explicitly stores topological relationships among neighboring polygons in the Arc Attribute Table (AAT) by storing the adjacent polygon IDs in the LPoly and RPoly fields. Adjacent lines are connected through nodes, and this information is stored in the arc-node table. The ArcInfo commands, CLEAN and BUILD, enforce planar topology on data and update topology tables.
Over the past two or three decades, the general consensus in the GIS community had been that topological data structures are advantageous because they provide an automated way to handle digitizing and editing errors and artifacts; reduce data storage for polygons because boundaries between adjacent polygons are stored only once; and enable advanced spatial analyses such as adjacency, connectivity, and containment. Another important consequence of planar enforcement is that a map that has topology contains space-filling, nonoverlapping polygons. Consequently, so-called cartographic (i.e., nontopological) data structures are no longer used by mainstream GIS software.
What Is Topology?
In 1736, the mathematician Leonhard Euler published a paper that arguably started the branch of mathematics known as topology. The problem that led to Euler's work in this area, known as "The Seven Bridges of Königsberg," is described in the accompanying article "Conundrum Inspires Topology." More recently, the United States Census Bureau, while preparing for the 1970 census, pioneered the application of mathematical topology to maps to reduce the errors in tabulating massive amounts of census data. Today, topology in GIS is generally defined as the spatial relationships between adjacent or neighboring features.
Mathematical topology assumes that geographic features occur on a two-dimensional plane. Through planar enforcement, spatial features can be represented through nodes (0-dimensional cells); edges, sometimes called arcs (one-dimensional cells); or polygons (two-dimensional cells). Because features can exist only on a plane, lines that cross are broken into separate lines that terminate at nodes representing intersections rather than simple vertices.
In GIS, topology is implemented through data structure. An ArcInfo coverage is a familiar topological data structure. A coverage explicitly stores topological relationships among neighboring polygons in the Arc Attribute Table (AAT) by storing the adjacent polygon IDs in the LPoly and RPoly fields. Adjacent lines are connected through nodes, and this information is stored in the arc-node table. The ArcInfo commands, CLEAN and BUILD, enforce planar topology on data and update topology tables.
Over the past two or three decades, the general consensus in the GIS community had been that topological data structures are advantageous because they provide an automated way to handle digitizing and editing errors and artifacts; reduce data storage for polygons because boundaries between adjacent polygons are stored only once; and enable advanced spatial analyses such as adjacency, connectivity, and containment. Another important consequence of planar enforcement is that a map that has topology contains space-filling, nonoverlapping polygons. Consequently, so-called cartographic (i.e., nontopological) data structures are no longer used by mainstream GIS software.
1 comment:
It is lovely - and we could certainly all do with a bit of creative relaxation at this time of year !!Good luck on the giveaway!! Thanks for coming by..best hosting company for small business
Post a Comment