WFM 6202: Remote Sensing and GIS in Water Management Geographic Information System (GIS) Lecture-3 Input of Geospatial Data Dr. A.K.M. Saiful Islam Institute of Water and Flood Management (IWFM) Bangladesh University of Engineering and Technology (BUET) November, 2015

Data Acquisition As data acquisition or data input of geospatial data in digital format is most expensive (about 80% of the total GIS project cost) and procedures are time consuming in GIS, the data sources for data acquisitions should be carefully selected for specific purposes.

Required Data Sources for GIS Analog maps Topographic maps with contours and other terrain features and thematic maps with respect to defined object classes are digitized by digitizers manually or by scanners semi-automatically. Aerial photographs Analytical or digital photogrammetry is rather expensive but the best method for updating Satellite image Satellite images or data are available for land use classification, digital elevation model (DEM), updating highway network etc. Ground survey with GPS Total station together with GPS (Global Positioning System) will modernize the ground survey. Reports and publications Social economic data are usually listed in the reports of statistics and census with respect to administration units.

Compare data acquisition methods

Rasterization Conversion between raster and vector data is very useful in practical applications of GIS. Rasterization refers to conversion from vector to raster data. Raster format is more convennient to produce color coded polygon maps such as color coded land use map, while map digitizing in vector format is more easier to trace only the boundary. Rasterization is also useful to integrate GIS with remote sensing becaues remote sensing images are in raster format.

Conversion Vector to Raster trapezoid area can be applied to convert vectorized polygon to rasterized polygon with grid cells

Vectorization Vectorization refers to conversion from raster to vector data, which is often called raster vector conversion.

Raster Vector Conversion Schematic of the raster vector conversion by which left and right polygons are identified