Getting Started with GIS

Now that you have learned all there is to know about how a GIS works, the real fun begins!

When beginning a project there are four things you need to know:

  • Purpose for building the project

The project should be defined in its objectives and outreach. For example, if you’re building a school then you need to find a location which is densely populated and has easy access to the whole area.

  • Information relevant to the purpose

Continuing with the example of the school, a map of the city with population density of areas and all roads and routes will help us decide the location.

  • Data input to the GIS.

All the relevant data needs to be given to the system so it can create a graphic. In our example, we will need the city and town borders, roads and railroads and population density of residential areas. The map is created with these parameters as three layers.

layers

  • Functions to be applied on data.
  • Create a new attribute and assign Boolean values to mark its presence on the map.
  • Remove boundaries between areas that have been assigned the same value.
  • Choose specific objects from the already created attributes.
  • Create buffers of a fixed width around previously specified line objects.
  • Create a new layer by overlaying two layers.
  • Measure the area of objects and give values.
  • Alter attributes using Boolean logics.
  • Generate a plot using the layers (attributes) and various shading and labeling techniques.
  • Generate a list of all the objects within a certain set of values.

Issues Faced When Working on a Project

With great complexity the number of problems that can arise increase. Commonly faced issues are related to management, data and functions used.

Management Concerns

Companies and agencies need quick results but it takes time to integrate all the data into the system to create the end product. Instructions from the managers may change mid-project and the whole thing needs to be started from scratch.

Data Handling

At times the data we need to get started is not available. This introduces another cumbersome task to the schedule. Data needs to be acquired, compiled and planned before working on the system.

Another issue pertaining to data is that it might be inconsistent with the quality or compilation. Or it might be in a format which is unusable (i.e. raster where vector objects need to be used).

Complex Decision-making

The specifics of a certain attribute can be too complex and difficult to explain to accuracy. This affects the output of the system and the reliability of the information. Also the restrictions applied to find a suitable object can be too limiting and tedious.

flow

Finding a Suitable Option

The whole objective of a graph is to look up information. We can search a point, a line or an area using our GIS output to find the one that is most appropriate. Rules are applied to comb through the many layers and objects.

Through a process called cascading, the layers are merged to form a new one of suitability. The geographical search can be atomistic where the suitability depends on the properties of the space only or holistic i.e. suitability depends on properties of the space but also on its distance from other locations.

Importance and precedence is assigned to conflicting factors if they clash. This assignment is on the basis of Decision Theory. The importance every value of an attribute holds for the decision maker is the Single Utility Function (SUF) and the importance of every attribute (or a group of them) overall is the Multiple Utility Function (MUF). SUFs and MUFs are selected by the decision-makers from a variety of options.

The sensitivity of the results depends on the choices made. Decision-makers should be careful and informed when making their choices if it affects the suitability of the site. In principle, sensitivity is different than it is in practice. For example, cutting down trees is a major concern in principle but in practice, there may be no trees on site.

map


 

References:

http://hcl.harvard.edu/libraries/maps/gis/tutorials.cfm
http://www.gistutor.com/mapserver/3-beginner-mapserver-tutorials/7-how-to-generate-a-simple-map-using-mapserver-and-a-shapefile.html
http://webgis.wr.usgs.gov/globalgis/tutorials/what_is_gis.htm

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