This document discusses different types of overlay operations in GIS. There are two main types: raster overlay and vector overlay. Raster overlay combines the pixel values in raster maps using logical operators like OR, AND and NOT to produce a new output map. Vector overlay integrates feature attributes by applying logical rules when combining different map layers, such as polygon-on-polygon, line-in-polygon, or point-in-polygon overlays. Proximity operations can also be performed by creating buffer zones around features to analyze surrounding areas.
This document discusses different types of overlay operations in GIS. There are two main types: raster overlay and vector overlay. Raster overlay combines the pixel values in raster maps using logical operators like OR, AND and NOT to produce a new output map. Vector overlay integrates feature attributes by applying logical rules when combining different map layers, such as polygon-on-polygon, line-in-polygon, or point-in-polygon overlays. Proximity operations can also be performed by creating buffer zones around features to analyze surrounding areas.
This document discusses different types of overlay operations in GIS. There are two main types: raster overlay and vector overlay. Raster overlay combines the pixel values in raster maps using logical operators like OR, AND and NOT to produce a new output map. Vector overlay integrates feature attributes by applying logical rules when combining different map layers, such as polygon-on-polygon, line-in-polygon, or point-in-polygon overlays. Proximity operations can also be performed by creating buffer zones around features to analyze surrounding areas.
This document discusses different types of overlay operations in GIS. There are two main types: raster overlay and vector overlay. Raster overlay combines the pixel values in raster maps using logical operators like OR, AND and NOT to produce a new output map. Vector overlay integrates feature attributes by applying logical rules when combining different map layers, such as polygon-on-polygon, line-in-polygon, or point-in-polygon overlays. Proximity operations can also be performed by creating buffer zones around features to analyze surrounding areas.
Download as PPTX, PDF, TXT or read online from Scribd
Download as pptx, pdf, or txt
You are on page 1of 12
Overlay Operation
• This operation allows us to overlay multiple feature
classes to combine, erase, modify, or update spatial features, resulting in a new feature class. • New information is created when overlaying one set of features with another. • There are basically two different types of overlay: (depending on the data structures) – Raster Overlay – Vector Overlay • The basic of overlay operation is logical operators: OR, AND, NOT, XOR Vector Overlay • More Difficult and Complex Processing • During vector overlay map features and associated attributes are integrated to produce new composite map. Logical rules can be applied to how the maps are combined. • It can be performed on different types of map features: { Polygon-on- Polygon, Line-in-Polygon, Point-in-Polygon} Raster Overlay • Less Difficult and Less Complex • During raster overlay, the pixel or grid cell values in each map are combined using arithmetic and Boolean operators to produce a new value in the composite map. Vector and Raster Overlay Operators • Logical: OR AND NOT • Conditional: == EQ <> NE <= LTE >= GTE < LT > GT • Arithmetic: + - * / ‸ A Small Practice: • Develop resulting attribute table when the following district road network is topologically overlaid on the district area map: Solution: Raster Overlay: HighValue-LowValue • Comparison of values in frame#1 and frame#2 • The highest value is picked for high value approach • The lowest value is picked for low value approach • The comparison is carried out on a grid cell by grid cell basis • Note: – High Value approach is for progressive activities – Low Value approach is for alternative activities Raster Overlay: HighValue-LowValue Raster Overlay: TopMap-BottomMap • For top map, assign a value in frame#3T to indicate where the highest value was found. • For bottom map, assign a value in fram#3B to indicate where the lowest value was found. • [If the highest value is found in frame#1, a 1 will be assigned; if the highest value is found in frame#2, a 2 will be assigned] in top map • [If the lowest value is found in frame#1, a 1 will be assigned; if the lowest value is found in frame#2, a 2 will be assigned] in bottom map • If the values are equal a 9 will be assigned. Raster Overlay: TopMap-BottomMap Proximity Operations (Buffer Zones) • It is used to create zones around selected geographic object in order to perform proximity analysis. • Area surrounding a specific object is evaluated • Types of Buffer: – Point Buffer – Line Buffer – Area Buffer