# IV - Computation report

The last step of the wizard is computation report, composed of 3 parts:

## 1 - Cartogram parameters

Lists user set and automatic parameters used for the transformation:

**Cartogram layer:**Name of the user-chosen transformed layer.**Cartogram attribute:**User-set variable determining the size of the cartogram.**Attribute type:**Type of the statistical variable used in step 3.**Transformation quality:**User-set (slider) general transformation quality, varying between 0 (low quality) and 100 (high quality).**Cartogram grid size:**Grid size used to seize the global transformation, defined automatically or user-set in the advanced options. (*see also*Advanced options – first grid)**Diffusion grid size:**Size of the grid used by the Gassner/Newmann diffusion algorithm, defined automatically or user-set in the advanced options. (*see also*Advanced options – second grid).**Diffusion iterations:**Number of runs of the Gassner/Newmann diffusion algorithm, defined automatically or user-set in the advanced options. (*see also*Advanced options – number of iterations).

## 2 - Cartogram layer & attribute statistics

Statistics pertaining to the main polygon layer and to the transformation variable:

**Number of features:**Number of polygons on the main polygon layer.**Attribute mean value:**Arithmetic mean of the user-chosen statistical variable.**Attribute minimum value:**Minimal value of the statistical transformation variable. N.B.: Negative values are not allowed. Zero values (which would induce a division-by-zero error in the algorithm) are automatically replaced by very small non-zero values.**Attribute maximum value:**Maximum value of the user-chosen statistical variable.

## 3 - Cartogram error indicators

The third part of the log shows several indicators evaluating the quality of the produced cartogram.

** A_{th}/A** is determined for each cartogram polygon, where

*A*

_{th}is the theoretical area that the polygon should have to be proportional to its value of the statistical variable, and where

*A*is its effective area. Expressed in %, the result can be interpreted as follows:

- A value inferior to 100% means that the polygon is larger than it should be.
*E.g.*the area of a feature with an*A*_{th}/*A*value of 80% should be reduced by 20% to be exactly proportional to its value of the statistical variable. [1.00/1.25 = 0.80 ; 1.00/(1.25-0.20×1.25) = 1.00] - A value superior to 100% mans that the polygon is smaller than it should be.
*E.g.*the area of a feature with an*A*_{th}/*A*value of 120% should be reduced by 20% to be exactly proportional to its value of the statistical variable.

*A*

_{th}/

*A*indice is calculated individually for each polygon. Four global indices of overall cartogram quality are shown in the log output:

**Mean cartogram error:**Arithmetic average of the*A*_{th}/*A*indicator for all features.**Standard deviation:**Standard deviation of the*A*_{th}/*A*indicator for all features.- For percentile calculation, features have been ordered by their
*A*_{th}/*A*values. The log shows the following percentiles:**25th percentile:**25% of the features have an*A*_{th}/*A*value inferior to this number.**50th percentile (or median):**50% of the features have an*A*_{th}/*A*value inferior to this number.**75th percentile:**50% of the features have an*A*_{th}/*A*value inferior to this number.

**Features with mean error +/- 1 standard deviation:**Number of features with an*A*_{th}/*A*diverging form average error by less than one standard deviation.**Computation time**: Difference between computation start-time and computation end-time.