How many immigrants does South Africa have? That depends who you ask.

Immigration is a hot-button issue in South African politics, but one of the most important questions about migrants remains the most basic: How many are there?

• A version of this post ran on the author's blog, Africa in Transition. The views expressed are the author's own.

South Africans often assume that since the end of apartheid and the coming of democracy in 1994, there has been a huge wave of migration into their country from the rest of the continent. Stories abound of entire Johannesburg neighborhoods that are now Nigerian or Congolese – and of immigrants taking over certain crime syndicates. Over the past five years, there have been multiple waves of xenophobic riots against Zimbabwean refugees in South Africa who, with the benefit of high education standards in their home country, are seen by township dwellers as competition for scarce jobs. 

But how many immigrants does South Africa really have? That depends on who you ask. 

The country's Human Sciences Research Council once estimated that there are 4 to 8 million undocumented migrants in South Africa, but later withdrew the figure. Those numbers nonetheless still make their way into the press – and the public consciousness – despite the fact that Statistics South Africa, a government agency, estimates undocumented persons in the country to be somewhere in the range of 500,000 to 1 million.

Using other demographic data, however, a team of academics at the Forced Migration Studies Program (FMSP) at the University of the Witwatersrand in Johannesburg has produced their own set of statistics. They estimate that the overall foreign population in South Africa ranges from 1.6 to 2 million, or 3 to 4 percent of the total population. They also report that there are between 1 and 1.5 million legal and illegal Zimbabwean immigrants in South Africa.

Because of its stability, highly developed infrastructure and first-world amenities, many elites from Nigeria, Congo, and other African countries travel to South Africa, and the wealthiest often have houses there. They are a population of high visibility. So too are the receptionists and others, born in Zimbabwe, who deal with the public. But South Africa has a total population of more than 50 million, and the numbers of these highly visible migrants are relatively small. Most immigrants, on the other hand, work in low-wage and informal sectors of the economy, filling the ranks of the country's security guards, street hawkers, and domestic workers. 

For sake of comparison, about 11 percent of the US population is made up of immigrants, according to the Center for Migration Studies.