Expressions
This page helps you to understand how to use the expressions in the Dashboard widgets. You can enter expressions in the Numbers, Categories, and Pie chart widgets. We're listing and describing the expressions that you could use in GOAT.
They work the same way as in QGIS, and by combining them you can compute more complex calculations or filter your data.
info
When referring to a field, insert it only in paratheses: (FieldName).
Numeric functions
The following functions work with number fields only. The input and the output will be numeric values.
| Expression | Function | Example |
|---|---|---|
| abs(x) | returns the absolute value of a number | = 5 |
| sqrt(x) | returns the square root of a number | = 4 |
| pow(x, y) | raises x to the power of y | = 8 |
| exp(x) | returns e raised to the power of x | = 2,718... |
| ln(x) | natural logarithm (base e) of x, inverse of exp | = 2.303... |
| log10(x) | logarithm base 10 of x | = 2 |
| round(x, n) | rounds a number x to n decimal places | = 1.24 |
| ceil(x) | rounds up to the next whole numer | = 2 |
| floor(x) | rounds down to the previous whole numer | = 1 |
| pi | returns the value of π | = 3.142.... |
| sin(x) | returns the sine of x (radians) | = 0.841... |
| cos(x) | returns the cosine of x (radians) | = 0.541... |
| tan(x) | returns the tangent of x (radians) | = 0.932... |
| asin(x) | returns the arcsine of x (radians) | = 1.571... |
| acos(x) | returns the arccosine of x (radians) | = 1.047... |
| atan(x) | returns the arctangent of x (radians) | = 0.785... |
| degrees(x) | converts angle x from radians to degrees | = 57.296... |
| radians(x) | converts angle x from degrees to radians | = 3.142... |
| rand(x, y) | generates a random number between x and y | = 3.17 |
String functions
The following functions work with text fields only. The input and the output will be text values.
| Expression | Function | Example |
|---|---|---|
| length(string) | returns the number of characters in a string excluding space | = 8 |
| char_length(string) | returns the number of characters in a string including space | = 9 |
| upper(string) | converts all letters to uppercase | = WALKING |
| lower(string) | converts all letters to lowercase | = goat |
| trim(string) | removes leading and trailing spaces | = biking |
| ltrim(string) | removes spaces only on the left side | = biking |
| rtrim(string) | removes spaces only on the right side | = biking |
| substr(string, start, length) | returns a substring starting at start position with optional length | = mob |
| substring(string, start, length) | returns a substring starting at start position with optional length | = mob |
| left(string, n) | returns the leftmost n characters | = acce |
| right(string, n) | retunrs the rightmost n characters | = lity |
| replace(string, search, replace_with) | replaces all occurences of one substring with another | = bike lane |
| regexp_replace(string, pattern, replacement) | uses regular expressions to find and replace part of a text | = BusStop# |
| regexp_substr(string, pattern) | extracts the first substring that matches a regular expression pattern | = 45 |
| strpos(string, substring) | returns the position (index) where a substring first appears and returns 0 if not found | = 5 |
| concat(a,b...) | joins multiple strings or fields together |
Date time functions
The following functions work with date/time fields only. The input and the output will be date/time values.
| Expression | Function | Example |
|---|---|---|
| now() | returns the current date and time | = 2025-10-07 11:35:00 |
| age(date1, date2) | returns the time interval between two dates | = 25 years 3 mons 12 days |
| extract(part, date) | extracts a specific component from a date (year, month, day, hour, minute, second) | = 2025 |
| date_part(part, date) | similar to extract returns the specified part of a date | = 10 |
| mmake_date(year, month, day) | creates a date from numeric year, month, day | = 2025-10-08 |
| make_time(hour, minute, second) | creates a time from numeric hour, minute, second | = 14:30:00 |
| make_timestamp(year, month, day, hour, minute, second) | combines date and time into a timestamp | = 2025-10-08 14:30:00 |
| to_date(string, format) | converts a text string to a date using the given format | = 2025-10-08 |
| to_timestamp(string, format) | converts a text string to a timestamp using the given format | = 2025-10-08 14:30:00 |
| to_char(date, format) | converts a date or timestamp to a formatted text string | = '2025-10-08' |
Casting functions
The following functions convert a value from one type to another. The input and the output will be of different types.
| Expression | Function | Example |
|---|---|---|
| to_int(x) | converts x to an integer (whole number) | = 3 |
| to_real(x) | converts x to a real (decimal) number | = 3.9 |
| to_string(x) | converts x to a text string | = '25' |
Generic functions
The following functions work with any type of field. The input and the output will be of the same type.
| Expression | Function | Example |
|---|---|---|
| coalesce(x, y, ...) | returns the first non-null value from the given list of inputs | |
| nullif(x, y) | returns NULL if x equals y, otherwise returns x | = NULL |
Aggregate functions
The following functions work with any type of field. The input and the output will be of the same type.
| Expression | Function | Example |
|---|---|---|
| sum(field) | returns the total sum of all values in a field (or group) | = 15230 |
| avg(field) | returns the average (mean) value of a field | = 12.6 |
| min(field) | returns the smallest (minimum) value in a field | = 0.5 |
| max(field) | returns the largest (maximum) value in a field | = 18.2 |
| count(field) | returns the number of features or non-null values in a field | = 347 |
Metric unary functions
| Expression | Function | Example |
|---|---|---|
| $area | returns the area of a polygon feature in the layer’s coordinate units (e.g., m²) | = 12500 |
| ST_Area(geometry) | returns the area of a specified geometry; used in expressions with geometry functions | = 12500 |
| $length | returns the length of a line feature in layer units (e.g., meters) | = 275.3 |
| ST_Length(geometry) | returns the length of a given geometry (line or polygon boundary) | = 275.3 |
| perimeter | returns the perimeter length of a polygon feature | = 490.6 |
| ST_Perimeter(geometry) | returns the perimeter of a geometry, similar to perimeter() but following the PostGIS standard naming | = 490.6 |
Metric buffer function
| Expression | Function | Example |
|---|---|---|
| buffer(geometry, distance) | creates a polygon buffer around a geometry at the specified distance (in layer units, e.g. meters) | = Polygon representing a 100 m buffer area |
Geometry unary functions
| Expression | Function | Example |
|---|---|---|
| centroid(geometry) | returns the center point (geometric middle) of a feature | = Point(13.41, 52.52) |
| ST_Centroid(geometry) | same as centroid(), follows PostGIS naming convention | = Point(13.41, 52.52) |
| convex_hull(geometry) | creates the smallest convex polygon that encloses all parts of a geometry | = Polygon(...) |
| ST_ConvexHull(geometry) | same as convex_hull(), using PostGIS syntax | = Polygon(...) |
| envelope(geometry) | returns the minimum bounding rectangle of a geometry | = Polygon((xmin, ymin), (xmax, ymax)) |
| ST_Envelope(geometry) | same as envelope(), in PostGIS form | = Polygon(...) |
| make_valid(geometry) | fixes invalid geometries (e.g. self-intersections, gaps) | = Polygon(...) |
| ST_MakeValid(geometry) | same as make_valid(), PostGIS version | = Polygon(...) |
| is_empty(geometry) | returns TRUE if geometry has no spatial content | = FALSE |
| ST_IsEmpty(geometry) | same as is_empty(), PostGIS form | = FALSE |
| is_valid(geometry) | returns TRUE if geometry is valid | = TRUE |
| ST_IsValid(geometry) | same as is_valid(), PostGIS version | = TRUE |
| x(geometry) | returns the X-coordinate of a point geometry | = 13.405 |
| ST_X(geometry) | same as x(), PostGIS version | = 13.405 |
| y(geometry) | returns the Y-coordinate of a point geometry | = 52.520 |
| ST_Y(geometry) | same as y(), PostGIS version | = 52.520 |
| xmin(geometry) | returns the minimum X-coordinate (left boundary) of a geometry | = 13.30 |
| ST_XMin(geometry) | same as xmin(), PostGIS syntax | = 13.30 |
| xmax(geometry) | returns the maximum X-coordinate (right boundary) of a geometry | = 13.50 |
| ST_XMax(geometry) | same as xmax(), PostGIS syntax | = 13.50 |
| ymin(geometry) | returns the minimum Y-coordinate (bottom boundary) of a geometry | = 52.45 |
| ST_YMin(geometry) | same as ymin(), PostGIS version | = 52.45 |
| ymax(geometry) | returns the maximum Y-coordinate (top boundary) of a geometry | = 52.55 |
| ST_YMax(geometry) | same as ymax(), PostGIS version | = 52.55 |
Here are some examples of combined expressions for more complex calculations: https://github.com/plan4better/goat/blob/main/apps/core/src/core/expression_converter.py
tip
Find further information in the QGIS documentation.