cell based gis working with raster

DCP 2002 Introduction to GIS II, Sustainability and the Built Environment, College of Design, Construction and Planning, UF

Week 2

Cell – based GIS

Working with raster


topics of the week

More on types of Functions in Raster

Data Conversion (vector & raster)

Solving Spatial Problems – Conceptual Model

A Sample Spatial Problem - Creating a Suitability Map


Data conversion

Converting from Features to Rasters

Polygons, Polylines, Points

Converting from Rasters to Features

Polygons, Polylines, Points

From any type of source file: CAD, Coverage, Shapefile, etc

Converting features using both string and numeric fields


Data conversion

RASTER TO VECTOR

VECTOR TO RASTER


Data conversion

Converting point features to raster

When you convert points, cells are given the value of the

points found within each cell. Cells that do not contain a

point are given the value of NoData. If more than one

point is found in a cell, the cell is given the value of the

first point it encounters when processing. Using a

smaller cell size during conversion will alleviate this.


Data conversion

Converting raster to point features When you convert a raster representing point features

to point features, for each cell of the input raster, a point will be created in the output. The points will be positioned at the centers of cells that they represent. NoData cells will not be transformed into points.


Data conversion

Converting polygon features to raster

When you convert polygons, cells are given the value

of the polygon found at the center of each cell.


Data conversion

Converting raster to polygon features

When you convert a raster representing polygonal

features to polygon features, the polygons are built from

groups of contiguous cells having the same cell values.

Arcs are created from cell borders in the raster.

Continuous cells with the same value are grouped

together to form polygons. Cells that are NoData in the

input raster will not become features in the output

polygon feature.


Data conversion

Converting polyline features to raster When you convert lines, cells are given the value of the line that

intersects each cell. Cells that are not intersected by a line are given the value of NoData. If more than one line is found in a cell, the cell is given the value of the first line it encounters when processing. Using a smaller cell size during conversion will alleviate this.


Data conversion

Converting raster to polyline features

When you convert a raster representing linear features to polyline features, a polyline is created from each cell in the input raster, passing through the center of each cell. Cells that are NoData in the input raster will not become features in the output polyline feature.


Solving spatial problems - conceptual model


Spatial problems – conceptual model

Step 1 – State the problem – your goal

Step 2 – Break the problem down – your objectives

Step 3 – Explore input datasets – establish relationships

Step 4 – Perform Analysis – define tools, methods, parameters

Step 5 – Verify the model’s results – go back if needed, refine

Step 6 – Implement the results – time to go real


A sample problem - creating the suitability map

Step 1: Goal

Find a best site to locate a new school.

Step 2: Set objectives to achieve this goal

1. Stay away from existing schools

2. Stay close to nearby recreational facilities

3. Build on suitable land use


Step 3: Collect, explore, set parameters, derive,

and create new datasets

1. Existing schools

2. Existing recreational facilities

3. Land use




Step 4: Perform analysis – rank the data

Rank areas close to recreation sites

SA > Straight Line Distance >> Reclass (10 – 1)

Rank areas away from existing schools

SA > Straight Line Distance >> Reclass (1 – 10)

Rank areas on suitable land use

SA > Select Suitable >> Reclass (1 – 10), the rest NoData



Step 4: Continue analysis – weight the data

Weight/prioritize all three layers

Dist. to Rec_sites - 0.5 weight

Dist. to Schools – 0.3 weight

Landuse – 0.2 weight

Combine all three layers into one single suitability map

Select spots with highest values



Step 5: Verify and go back to analysis if needed

Take a trip at the site and see if you have overlooked

smth, if a new building has been added since the time

your data was created! Perhaps time to re-define

parameters, re-think weighting criteria or nr of classes

and re-run analysis.

Step 6: Implement the results

Recommend to the decision makers the suitable locations

for building the new school!


Sample problem – creating a suitability map

COMPUTER DEMO

cell based gis working with raster

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