Google Earth Engine: Calculate protected areas with WDPA dataset

Question

I want to calculate protected areas in a region. My procedure was to convert the WDPA data set into an image and then calculate the area using the reducer.sum function. My problem is that my pixel value from Germany_PA is: constant: 0, so I could not use the reducer.sum function.

Is there a way to change the pixelvalue or is there another function to calculate the area?

Here is my code:

Map.setCenter(11.57, 50.88, 5);

var dataset = ee.FeatureCollection('WCMC/WDPA/current/polygons');
// WDPA Polygone filter
var target_values = ee.Filter.inList('DESIG', [ 'Nationalpark' ]);
  
var Nationalpark = dataset.filter(ee.Filter.and(
  (target_values),
  ee.Filter.eq('MARINE', '0')))
  
var gaul = ee.FeatureCollection("FAO/GAUL_SIMPLIFIED_500m/2015/level1")
var Germany = gaul.filter(
  ee.Filter.eq('ADM0_NAME', 'Germany'))
  
var PA = ee.Image().float().paint(Nationalpark)

// Nationalpark in Germany
var Germany_PA = PA.clip(Germany)

Map.addLayer(Germany_PA,{palette: ['00FF00']} , 'Germany_PA')

Answer 1

It doesn't matter. Calculation of ee.Image.pixelArea() can be forced to consider only the masked area with value equal 0 by using 'mask(ee.Image(PA).eq(0)' method. An example looks as follows:

var area = ee.Image.pixelArea().mask(ee.Image(PA).eq(0)).reduceRegion({
    reducer: ee.Reducer.sum(),
    geometry: Nationalpark_GE,
    scale: 500,
    maxPixels: 1e13
    
});

Modifying your code for also including Germany area calculation (for comparison purpose) I got:

Map.setCenter(11.57, 50.88, 5);

var dataset = ee.FeatureCollection('WCMC/WDPA/current/polygons');

// WDPA Polygone filter
var target_values = ee.Filter.inList('DESIG', [ 'Nationalpark' ]);
  
var Nationalpark = dataset.filter(ee.Filter.and(
  (target_values),
  ee.Filter.eq('MARINE', '0')));
  
print("Nationalpark", Nationalpark);

var gaul = ee.FeatureCollection("FAO/GAUL_SIMPLIFIED_500m/2015/level1");

var Germany = gaul.filter(
  ee.Filter.eq('ADM0_NAME', 'Germany'));

var Nationalpark_GE = ee.FeatureCollection(Nationalpark).filterBounds(Germany);

print("Nationalpark_GE", Nationalpark_GE);
  
var PA = ee.Image().float().paint(Nationalpark);

// Nationalpark in Germany
var Germany_PA = ee.Image(PA).clip(Germany);

var area = ee.Image.pixelArea().reduceRegion({
    reducer: ee.Reducer.sum(),
    geometry: Germany,
    scale: 500,
    maxPixels: 1e13
    
});

print("Germany Area", area.get('area'));

var area = ee.Image.pixelArea().mask(ee.Image(PA).eq(0)).reduceRegion({
    reducer: ee.Reducer.sum(),
    geometry: Nationalpark_GE,
    scale: 500,
    maxPixels: 1e13
    
});

print("National Parks Germany Area", area.get('area'));

Map.addLayer(Germany_PA, {palette: ['red']} , 'Germany_PA');
Map.addLayer(Nationalpark_GE, {color: 'blue'} , 'Nationalpark_GE');

Running above lines in GEE code editor, I got the result of following picture where the area of the parks (blue color) is considerably smaller than that of Germany.