Data Calculator Instructions

Content-

Basic Information
Entering an Equation
Operators
Datasets with Time Series Layers
Map and Data Controls
Examples

Appendices-

• Country FIPS codes
• US State Codes
• River Basin codes
• Continent codes

Basic Information

Data Calculator allows a user to execute algebraic and logical expressions/equations over any number of the gridded datasets in the system on the fly and display results in a form of map and histogram and/or download these results as an ASCII data (AAIGrid format). The calculations are performed on the grid cell level over the map extends chosen by a user in the main window.

"Equation" input form-
The equation has to be entered in this  input form and it can contain basic and advanced mathematical functions, conditional operators explained below in the Operators section. A set of special instructions could be used to control the calculation results and graphical design of the result visualization by the map and the histogram. This instructions are accessible via fold-out menus named Map Options, Data Options, and Color Options.

"Integral" input form-
An equation entered in this input form is integrated over map extent area in per km² units. Integration is performed only over pixels/area where integration equation returns a real number and skips pixels where any involved in the integration dataset has nodata value (-9999) or the equation return "illegal operation" result such as division by zero, etc.  The integration results are displayed as a text in the histogram area of the calculation results graphics.

Entering an Equation

Equation has to present a valid mathematical and/or logical expression that contain a combination of variables and operators. In the case of this Calculator variables are numerical gridded datasets as the calculations are applied to each of their grid cells/pixels. Dataset notations (symbols) cold be found in the Dataset Table which are usually grouped by theme and accessible radio button switches. For the user convenience, mouse clicking on the symbols in the Dataset Table automatically enters them to the active Equation or Integral input line at the active caret position. This ensures that the symbol is not misspelled as it is also case sensitive. Of course, a user can type in dataset symbols directly. For example, a very simple calculation to convert elevation from meter to kilometer units could be done by this equation Elev/1000 where symbol "Elev" represents the elevation dataset.

Operators

Alrthmetic Operators-

Logical Operators-

Mathematical Functions-

Datasets with Time Series Layers

Single Layer Referencing-
Datasets with Time Series Layers (TSL) are indicated by a star (*) symbol in the Data Table. Each layer can be a accessed via TSL identifier in a form {YYYY-MM-DD}. For example, a difference in Sea Surface Temperature between two dates (summer and winter) could be calculated by this equation-

SST{2007-07-15} - SST{2007-12-15}
a). In the case of this equation a user can enhance resulting map color range by setting  Map Options -> Min = -10 and Map Options -> Max = 20. It is also recommended to use global map extend.

If no TSL identifier is provided for a given time series dataset than the latest (last) data layer is used in the equation, e.g. equation

(SST * 1.8) + 32

converts sea surface temperature from Celsius to Fahrenheit for the latest data layer in SST dataset. And if a user want to do the same for some specific date, say November 12, 2007 then it could be done with this formula-

(SST{2007-11-12} * 1.8) + 32

Range of Layers Referencing-
A syntax to call a range of Time Series Layers (TSL) is provided by a double dot operator in the form of {YYYY-MM-DD..YYYY-MM-DD} where the first data has to be earlier than the second date after the double dot operator. The double dot operator returns an array of layers so that array functions could be used on them (such as min(), max(), average(), sum(), map(), etc.). For example, a number of days with precipitable atmosphere moisture over 100 mm in the month of July, 2007 could be calculated with this equation-

sum( map($_>50, PrecipN{2007-07-01..2007-07-31}) )
a). Attention- Symbol $_ used in this equation references each element in the array PrecipN{2007-07-01..2007-07-31} by the map() function.
b). In the case of this equation a user can enhance resulting map color range by setting  Map Options -> Min = 1 and Map Options -> Max = 15. It is also recommended to use global map extend.
c). Caution- Avoid to use equations that require too many data layers to be called (31 data layers are called in this example) as it might take a longer time to perform this computation.

Time Series Layer Types-
Different time series types are referenced by their specific form of referencing indicated in the table below-

The logic of the date syntax is that it is the same format for all (XXXX-XX-XX) where zeroes denote something that is not available as, say, days in the monthly datasets.

Map and Data Controls

Map Options Tab-
It has two controls-

1. Set Range inputs- Sets min and max range for the resulting calculations. Sometimes it could be used to cut out outliers from the results which enhances the colors for the map and histogram. Example that shows lowlands with elevation between 0 and 300 m,
   
   Elev
   Map Options -> Min = 0 and Map Options -> Max = 300
    
2. Use Log Scale checkbox- Displays results in a logarithmic scale. It is very useful to display calculator resulting datasets in a log scale if the data range lays within multiple orders of magnitude across map pixels. For example, population increase between year 2015 and 1990-
   
   Pop15 - Pop90 (use for both Equation and Integral inputs; use map in Global extent)
   Map Options -> Use Log Scale = checked
   
   The results show an average increase of 15.3 people/km² and total increase (result of integration) of 2.7 billion people in Global extent.

Data Options Tab-
It has three controls-

1. Ignore Illegal Math checkbox (checked by default)- It converts grid cell values to nodata value (-9999) where equation returns illegal mathematical operation codes such as division by zero, logarithm or square root of negative number, etc. If it is unchecked and an illegal math occurs in any grid cell/pixel the Calculator return an error for the whole dataset.
    
2. High Resolution Interpolation checkbox- The system uses a higher data resolution of data for the map extent (640x480 grid cells) instead of the default values of 320x240 grid cells. The higher resolution might take some longer time to complete the calculations, but can result in more details on the map.
    
3. Get Results as Data checkbox- The resulting dataset is returned as a ASCII Unicode data file in AAIGrid format for download or display as it is de facto the most common non-binary (text) gridded data format around.

Color Options Tab-
It has only one control at this time-

1. Legend radio button group- It gives user a choice between Grayscale (B/W) and Rainbow color palettes for the resulting map and histogram. More palettes will be added in future.

Examples

Appendices

Country FIPS codes-

Usage example- Population-2000 of China where 46 is country ID code for China-

Pop00 if Country == 46
Map Options -> Use Log Scale = checked.
Use in both Equation and Integral inputs.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

US State FIPS codes-

Usage example- Population-2000 of New Hampshire where 33 is state ID code for NH-

Pop00 if State == 33
Map Options -> Use Log Scale = checked.
Use in both Equation and Integral inputs.

River Basin codes-

River (Watershed) Basins only with area over 100,000 km² are referenced in the table below (about 150 basins). Total number of basins in RiverB dataset is over 10,000. So other basin IDs could be found by mouse over data reading on the main map above the Calculator.

 Usage example- Population-2000 in Indus Basin where 26 is this basin ID code-

Pop00 if RiverB == 26
Map Options -> Use Log Scale = checked.
Use in both Equation and Integral inputs.

Continent codes-

 Usage example- Population-2000 in Africa where 1 is its ID code-

Pop00 if Cont == 1
Map Options -> Use Log Scale = checked.
Use in both Equation and Integral inputs.

Close this page