Something like this would do the trick

getCountriesListNights(){
  const r = this.http.get<any>(this.APIUrl + "/WorldMapDataNights?&year=" + this.selectedYear + "&month=" + this.selectedMonth +"&gender=" + this.selectedGender + "&age="+this.selectedAge + "&quarter=" + this.selectedQuarter).pipe(map((res) => {return res.map((res: { id: any; countryName: any; value: any; year: any; name: string; multiPolygon: any[] }) =>({countryName: res.countryName,  id: res.id,  value: res.value, year: res.year, name: res.name, multiPolygon: res.multiPolygon  }))})).subscribe(res =>{
    console.log(res);
    this.renderMapObject(res);
    this.http.get<any>(this.APIUrl + "/yourSecondApiURL").subscribe(otherapiRes =>{
      const finalResult = res.value / otherapiRes .value;
      console.log(finalResult);      
    }
  });
};

it is not pretty and you could use something like

const res = await this.http.get<any>("...firstApiUrlAndMapping...").toPromise();
const res2 = await this.http.get<any>("...secondApiUrlandMapping...").toPromise();
finalResult = res.value/res2.value;
 

but both ways should work just fine.

EDIT

A basic example of running two http calls inside each other would be

const res = this.http.get<any>('https://reqbin.com/echo/get/json').subscribe(res =>{
  console.log(res);
  this.http.get<any>('https://reqbin.com/echo/get/json').subscribe(otherapiRes =>{
    console.log(otherapiRes);
    console.log('Both Results:' + res.success + ' -- ' + otherapiRes.success);
  });
});

Okay, to achieve the aim, you need a fulfilled response from two sources. In general, the Promise.all() is giving what you need.

There are several ways to achieve your need in RxJS world. For example, the operator zipWith returns a stream that notifies of an array of results (its source and its argument inputs).

A sample you can play with:

of('Foo')
  .pipe(
    delay(1000),
    tap(() => console.log('Foo succeeded')),
    zipWith(
      of('Bar').pipe(
        delay(2000),
        tap(() => console.log('Bar succeeded'))
      ),
      of('Baz').pipe(
        delay(2500),
        tap(() => console.log('Baz succeeded'))
      )
    ),
    // You can process and transform the outcome
    map(([foo, bar, baz]) => foo + bar + baz)
  )
  .subscribe(result => {
    console.log('All succeeded:', result);
  });

https://stackblitz.com/edit/rxjs-er8zx1?file=index.ts